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Article

Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism

by
Yuyan Zhao
1,2,
Hanwen Luan
1,
Binghan Yang
1,
Zhenghe Li
1,
Meitong Song
1,
Bing Li
1,2 and
Xiaodan Tang
1,2,*
1
College of Geo-Exploration Science and Technology, Jilin University, Changchun 130026, China
2
Institute for Black Soils, Jilin University, Changchun 130026, China
*
Author to whom correspondence should be addressed.
Water 2023, 15(4), 767; https://doi.org/10.3390/w15040767
Submission received: 4 January 2023 / Revised: 13 February 2023 / Accepted: 13 February 2023 / Published: 15 February 2023
(This article belongs to the Special Issue Geochemistry of Water and Sediment III)
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Abstract

:
The rational utilization of solid waste has always been a worldwide concern. In this study, coal fly ash (CFA) and red mud (RM) were used in combination to synthesize efficient heavy metal adsorbents. A new way of resource recycling was provided with the collaborative reuse of CFA and RM. To obtain the modified composite materials, CFA and RM were mixed and melted in three ratios. After modification, these materials were then utilized to adsorb Pb, Cu, and Cd in water in both single and ternary systems. The physicochemical properties of CFA, RM, and three modified composite materials were measured by X-ray diffraction analysis, energy dispersive X-ray spectroscopy, scanning electron microscope, Fourier transform infrared spectroscopy, vibrating sample magnetometer, surface area analyzer, and porosity analyzer. In the single and ternary systems, the effects of the modified composite material dosage, solution pH, initial concentration of heavy metals, and adsorption time were discussed, and the results were better fitted with the Langmuir isotherm and the pseudo-second-order kinetic. It was discovered that the modified composite materials had a greater specific surface area (63.83 m2/g) than CFA and RM alone, as well as superior adsorption capacity and magnetic characteristics. The adsorption capacities of C1R4 for Pb, Cu, and Cd were 149.81 mg/g, 135.96 mg/g, and 127.82 mg/g in the single system, while those of Cu and Cd decreased slightly in the ternary system, and the preferential adsorption order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. Among the three modified composite materials, C1R4 had the best adsorption capacity.

1. Introduction

With accelerated economic growth, the issue of environmental contamination is getting more serious. When industrial waste is thrown in large quantities into surrounding water bodies, it degrades water quality, pollutes the water, stresses the ecosystem, and even endangers human health [1]. Water contamination is extremely hazardous and hard to control, especially when it contains heavy metals. Heavy metals are considered to be very hazardous contaminants because of their pathogenicity across the food chain [2]. The heavy metals Pb, Cu, and Cd have attracted a great deal of interest due to their widespread creation and release into the aquatic environment [3]. According to data released by the World Health Organization (WHO) and the Environmental Protection Agency (EPA), the highest permitted levels for Pb, Cu, and Cd in drinking water are 0.01 mg/L, 2 mg/L, and 0.003 mg/L, respectively. Once the human body ingests excessive heavy metals, it may do serious damage to our bodies and even cause death [4].
Over the past few decades, several remediation techniques for heavy metal contamination in water have been developed, including chemical precipitation [5], electrochemical [6], ion exchange [7], membrane technology [8], and reverse osmosis [9]. The adsorption method is regarded as an inexpensive and efficient water treatment technology that is widely utilized [10]. Many adsorbents, such as activated carbon [11], clay minerals [12], biological substances [13], zeolites, and some industrial solid wastes [14], have been extensively utilized in the removal of heavy metals from water.
Red mud (RM) is a reddish-brown solid waste generated during the mining of bauxite [15], and coal fly ash (CFA) is a powdery mineral residue formed as a byproduct of coal combustion [16]. Their output is enormous; simply stacking them will lead to environmental pollution. It has always been a focus of study to increase the comprehensive utilization rate of solid waste resources. In the past several years, RM and CFA have often been used as adsorbents to remove heavy metals. For example, when RM was modified with amorphous MnO2, its specific surface area reached 38.91 m2/g, and its maximum equilibrium capacity for Cd was 103.59 mg/g [17]. A granular RM supported by zero-valent iron was successfully prepared, and its maximum removal capacity for Pb was 149.42 mg/g [18]. The remediation efficiency of Cu by modified RM was 78.1% [19]. Modified CFA had maximum uptake capacities for Pb and Cd of 126.55 mg/g and 56.31 mg/g, respectively [20]. In addition, Al2O3 and SiO2 are the primary active ingredients in both CFA and RM; different proportions of these two ingredients combined can produce the diverse radioactivity of Si and Al [21], and the abundant presence of Fe2O3 in RM can be used to synthesize magnetic material without the utilization of additional magnetic nanoparticles. CFA and RM are often used as raw materials to synthesize zeolite when used alone, but they are more often used to synthesize asphalt materials when used in combination [22]. This research aims to offer a novel resource recycling strategy for CFA-RM synergistic reuse; that is, CFA and RM will be composed and modified into an effective heavy metal adsorbent, whose adsorption effectiveness is expected to surpass that of CFA and RM by themselves, and heavy metals in water can be efficiently and cheaply removed by this co-processing method.
In this study, CFA and RM were combined in three different ratios by the alkali melting method to synthesize modified composite materials that were used to remove heavy metals from the water body. The effects of the initial concentration of heavy metals, adsorbent dosage, adsorption time, temperature, and the solution pH on the removal rate and equilibrium adsorption capacity of heavy metals were investigated, and the adsorption process and mechanism were presented by a series of heavy metal adsorption simulation studies. Since there are multiple heavy metal ions competing with each other in the actual polluted water, all experiments were performed in both single and ternary systems. To measure the chemical and physical performance of samples, the techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and surface area and porosity analyzer (BET) were applied.

2. Materials and Method

The schematic diagram of CFA-RM modified composite material preparation, performance characterization, and adsorption analysis is shown in Figure S1.

2.1. Experiment Materials and Instruments

CFA and RM were acquired from a coal-fired power station in Jilin City and a company in Guangxi City, respectively. The main mineral compositions of the CFA were quartz and mullite, and those of the RM were hematite, goethite, pyrite, and gibbsite, which were attained from the consequences of polycrystalline XRD (XD6, Persee, China). The principal compositions of the CFA were SiO2 (52.00 wt%), Al2O3 (24.60 wt%), Fe2O3 (3.74 wt%), and CaO (3.08 wt%), and those of the RM were SiO2 (25.80 wt%), Al2O3 (25.23 wt%), CaO (15.68 wt%), and Fe2O3 (7.02 wt%).
Absolute ethanol, sodium hydroxide (NaOH), and hydrochloric acid (HCl) were in guaranteed reagent grade. The water used in the experiment was ultrapure deionized water with a resistivity of 18.2 MΩ·cm at 25 °C. The 1000 mg/L national standard solutions of lead (Pb, GSB04-1742-2004), copper (Cu, GSB04-1725-2004), and cadmium (Cb, GSB04-1721-2004) were purchased from the National Center of Analysis and Testing for Nonferrous Metals and Electronic Materials. The different concentrations of Pb, Cu, and Cd solutions used in the experiment were obtained by the stepwise dilution method.
Samples were weighed with an electronic balance (ATY124, Shimadzu, Japan). The multi-head magnetic stirrer (HJ-6, Jintan Jiangnan, China), cyclotron oscillator (HY-8A, Jintan Jingda, China), muffle furnace (KBF1400, Laibu, China), pH meter (PHBJ-260, Leici, China), and centrifuge (TDL-5A, Anting, China) were used for the sample processing stage. The concentration of heavy metals was determined by an atomic absorption spectrometer (A3, Persee, China). The main mineral composition, chemical element, surface structure, functional groups, specific surface area, and magnetism of the sample are characterized by polycrystalline XRD (XD6, Persee, China), EDS (EDX6000B, Skyray, China), field emission SEM (JSM-7900F, JEOL, Japan), FTIR (Nicolet iS10, Thermo Scientific, Waltham, MA, America), a surface area and porosity analyzer (ASAP2020HD88, Mike, America), and a vibrating sample magnetometer (VSM-7900, Weipu, China), respectively.

2.2. Preparation of Modified Composite Material

There were many impurities in CFA and RM that needed to be pretreated before use. Therefore, CFA (or RM) was uniformly mixed with ultrapure deionized water in a 10% (w/v) ratio at room temperature, shaken at 120 rpm for 24 h, and centrifuged at 9000 rpm for 30 min. The obtained precipitate was washed sequentially with absolute ethanol and ultrapure deionized water, dried at 65 °C for 6 h, filtered through a 0.25-mm sieve, and kept in the desiccator for later use.
The resulting CFA and RM were mixed in three different proportions (4:1, 1:1 and 1:4) to synthesize three modified composite materials (C4R1, C1R1 and C1R4) with silicon-alumina ratios (0.95, 0.78 and 0.62) by alkali melting method, that is, C4R1, C1R1 or C1R4 was uniformly mixed with NaOH at a mass ratio of 5:8 in a nickel crucible, calcined at 300 °C for 3 h, cooled, repeatedly washed NaOH on the surface, immersed in a specific amount of ultrapure deionized water for 48 h, separated from the liquid, dried, and screened through a 0.25-mm sieve.

2.3. Batch Sorption Experiments

A convex flask was filled with 50 mL of heavy metal solution at a specific concentration in the single or ternary system, and the initial solution pH was changed by 0.1 mol/L HCl or 0.1 mol/L NaOH according to the experimental conditions [23]. A specific quantity of modified composite material was poured into the above convex flask, shaken for a specified period of time at 180 rpm at a specific temperature, percolated through a 0.45-μm membrane for a later test.

2.3.1. Experimental Setup in the Single System

To study the influence of pH, it was set to 2, 3, 4, 5, 6, 7, 8 for Pb and Cd, and 1, 2, 3, 4, 5, 6 for Cu, with 0.10 g of C4R1, C1R1, or C1R4, 90 min of adsorption time, and 100 mg/L Pb, Cu, or Cd solution, respectively.
To analyze the impact of adsorbent dosage, C4R1, C1R1, or C1R4 were weighed at 0.05 g, 0.10 g, 0.20 g, 0.30 g, and 0.50 g with pH 6, 90 min of adsorption time, and 100 mg/L Pb, Cu, or Cd solution, respectively.
The adsorption kinetics studies were conducted at the adsorption time of 5 min, 10 min, 20 min, 30 min, 45 min, 60 min, 90 min, 120 min, and 180 min with pH 6, 0.10 g of C4R1, C1R1, or C1R4, and 100 mg/L Pb, Cu, or Cd solution, respectively.
The isothermal adsorption experiments were conducted at the initial Pb, Cu, or Cd solution concentrations of 10 mg/L, 20 mg/L, 50 mg/L, 100 mg/L, 200 mg/L, 300 mg/L, 400 mg/L, and 500 mg/L with pH 6, 0.10 g of C4R1, C1R1, or C1R4, 90 min of adsorption time at the temperatures of 25 °C, 35 °C, or 45 °C, respectively.

2.3.2. Experimental Setup in the Ternary System

To measure the impact of pH, it was set to 1, 2, 3, 4, 5, and 6 with 0.10 g of C4R1, C1R1, or C1R4, 90 min of adsorption time, and 100 mg/L mixed Pb, Cu, and Cd solution.
For evaluating the effect of adsorbent dosage, C4R1, C1R1, or C1R4 were weighed at 0.05 g, 0.10 g, 0.20 g, 0.30 g, and 0.50 g with pH 5, 90 min of adsorption time, and 100 mg/L mixed Pb, Cu, and Cd solution.
The adsorption kinetics experiments were performed at the adsorption time of 5 min, 10 min, 20 min, 30 min, 45 min, 60 min, 90 min, 120 min, and 180 min with pH 5, 0.10 g of C4R1, C1R1, or C1R4, and 100 mg/L mixed Pb, Cu, and Cd solutions, respectively.
The isothermal adsorption experiments were completed at the initial mixed Pb, Cu, and Cd solution concentrations of 10 mg/L, 20 mg/L, 50 mg/L, 100 mg/L, 200 mg/L, 300 mg/L, 400 mg/L, and 500 mg/L with pH 5, 0.10 g of C4R1, C1R1, or C1R4, 90 min of adsorption time at the temperatures of 25 °C, 35 °C, or 45 °C, respectively.
In brief, the batch sorption experiments were conducted by changing the modified composite material dosage, initial heavy metal concentration, solution pH, and adsorption time in the single or ternary system. The above values for modified composite material dosage, initial heavy metal concentration, solution pH, adsorption time, and experimental process were designed to combine the findings of the previous reports [18,20,24,25,26,27] and actual situations in the laboratory. The experimental data were analyzed and plotted by analysis of variance and regression using Excel and Origin. The coefficient of variation was mostly less than 1%. If the variation in element content exceeded 5%, an identical run would be undertaken, and closer data points would be used. All mean values are the averages of three independent samples. Blank and parallel controls were set in the experiment.

3. Results and Discussion

3.1. Material Characterization

3.1.1. SEM Analysis

The CFA, RM, C4R1, C1R1, and C1R4 were characterized by scanning electron microscopy. As shown in Figure 1a, the surface of CFA was dense, and the pores were poorly developed. Its main form was amorphous aluminosilicate glass spheres, and their sizes varied from a few microns to 30 microns [28]. The surface of RM was rough and porous; the particle size difference was significant, and the porosity was high (Figure 1b). The original lattices of CFA and RM were broken after well mixing and reacting NaOH at 300 °C, and the microstructure was changed to a porous structure with a rough exterior, which was similar to the crystallized zeolite structure. Numerous pores and particles could be detected on the surface of C4R1, C1R1, and C1R4 (Figure 1c–e), which promoted the expansion of the specific surface area of the particles. As the RM content increased, the porosity of the modified composite material increased.

3.1.2. EDS Analysis

The chemical elements of CFA, RM, C4R1, C1R1, and C1R4 were measured by EDS and shown in Table S1 and Figure 2. The main chemical elements of CFA were C, O, Si, and Al, and those of RM were C, O, Si, Al, and Fe. For C4R1, C1R1, and C1R4, their major chemical elements were still C, O, Si, Al, and Fe, but the element ratio was changed after modification. With the increase in the proportion of RM, the proportion of Fe in the element content increased accordingly. The rise of the Na peak indicated that the Na from NaOH was exchanged onto the surface of C4R1, C1R1, and C1R4 through modification.

3.1.3. BET Analysis

The specific surface of the adsorbent had the greatest effect on the adsorption capacity. The hysteresis curves of CFA, RM, C4R1, C1R1, and C1R4 were shown in Figure 3. When the relative pressure increased, the hysteresis curve of CFA remained flat, and its adsorption per unit mass did not vary considerably, indicating that CFA itself had fewer holes and a smaller specific surface area [29]. The specific surface area of CFA before modification was 0.68 m2/g. The adsorption per unit mass of RM, C4R1, C1R1, and C1R4 gradually increased with the increase of relative pressure, and the hysteresis curve was a type IV adsorption curve. The specific surface area of RM before modification was 33.02 m2/g, but Fe occupied more exchangeable sites than Al and Si, which made its adsorption performance low. After modification, the specific surface areas of C4R1, C1R1, and C1R4 were 29.66 m2/g, 32.51 m2/g, and 63.83 m2/g, respectively. Under the same relative pressure, the adsorption per unit mass of C1R4 was the largest, indicating that its pores were well developed and that it had the largest specific surface area. The more pores and active sites the material had, the stronger the adsorption performance. Comparing the pore size distributions and physical properties of CFA, RM, C4R1, C1R1, and C1R4 in Figure S2 and Table S2, it was also found that C1R4 might have the best adsorption capacity since its specific surface area and pore volume were the highest and its average particle diameter was the smallest.

3.1.4. FTIR Analysis

The FTIR spectra of CFA, RM, C4R1, C1R1, and C1R4 were presented in Figure 4, and the variations in bond locations and functional groups of raw materials and modified composite materials could be compared. In Figure 4a, the sharp peaks of CFA at 1080 cm−1 were caused by the symmetric vibration of TO4 (T = Si or Al) [30]. It was clear from the RM infrared spectra in Figure 4b that the 1650 cm−1 wavelength of RM indicated the H-OH bending vibration peak, and the sharp peaks at around 990 cm−1 may be due to the presence of the Si-O group in the RM spectrum [31]. The main chemical components of CFA and RM were SiO2 and Al2O3, and the peak positions of the functional groups were similar. At about 3450 cm−1, it was mainly expressed as the hydroxyl stretching vibration of Si-OH, the hydroxyl stretching vibration of Al-OH, and the stretching vibration of intermolecular hydrogen bonds, and the increase in its vibrational strength after modification was mainly related to the addition of NaOH. RM contained many carbonate compounds, as evidenced by the band at 1447.10 cm−1, which could be attributed to CO32−. However, after mixed modification, the CO32− peak in the modified composite material moved and decreased intensity [17]. Al-O stretching vibrations were at 992 cm−1, and Fe-O stretching vibrations were present at roughly 500 cm−1. In Figure 4c, the higher the RM proportion, the higher the peak vibration intensity of the modified composite material. Compared with CFA and RM, the decrease in the peak value of functional groups for C4R1, C1R1, and C1R4 indicated that a large number of chemical reactions occurred during the modification process, releasing a large number of active sites.

3.1.5. Magnetic Analysis

The hysteresis curves of CFA, RM, C4R1, C1R1, and C1R4 were shown in Figure 5. Their hysteresis curves all had an “S”-shaped structure, and with the increase in magnetic flux density, the magnetic susceptibility also increased gradually. It could be seen that the CFA itself had weak magnetic properties; as the magnetic susceptibility reached saturation, its maximum saturation susceptibility was about 0.7 emu/g. RM had a certain degree of magnetism; with the increase of magnetic induction, the magnetic susceptibility reached 5 emu/g, which had not yet reached saturation. The magnetic susceptibilities of C4R1, C1R1, and C1R4 were lower than those of RM, and C1R4, with the highest RM proportion, had the highest magnetic susceptibility.
There had been several studies on the separate modification of CFA and RM, but very few on their combined application in environmental protection. RM had an abundant active component, a large specific surface area, and the potential to synthesize zeolite. However, RM had a large proportion of Fe2O3, and some of the Al3+ in the silica-alumina framework of the synthetic zeolite was replaced by Fe3+, which caused the lattice to be distorted and reduced the synthetic zeolite’s crystallinity. Zeolite’s physicochemical qualities could also be harmed by Fe3+ being linked to its surface or interior as oxides. CFA also had numerous active components and the potential to synthesize zeolite; its main oxides were similar to those in RM, but the Fe2O3 content in CFA was low. As a result, when CFA was combined with RM, the overall system’s Fe2O3 content could be decreased along with its negative effects, while the system’s adsorption capacity could be improved. Additionally, the modified composite materials C4R1, C1R1, and C1R4 with better magnetic characteristics might be created without the addition of extra magnetic nanoparticles.

3.2. Adsorption Analysis in the Single System

3.2.1. Influence of the Dosage of C4R1, C1R1, and C1R4

In Figure 6, with the increase in the dosage of modified composite material, the equilibrium adsorption capacities of Pb, Cu, and Cd gradually decreased. The initial concentration and volume of heavy metals were constant, so the amount of ions in the solution remained constant. When the adsorbent dosage was low, most of the heavy metal ions were adsorbed and few adsorption sites were left, hence the adsorption capacity was high. As the adsorbent dosage gradually increased, more and more adsorbent and available adsorption sites remained, and thus the adsorption capacity gradually decreased, which was a waste for the adsorbent [32]. When the dosage was 0.05 g, the equilibrium adsorption capacities of C4R1 to Pb, Cu, and Cd were 99.75 mg/g, 73.9 mg/g, and 57.9 mg/g; those of C1R1 to Pb, Cu, and Cd were 99.80 mg/g, 78.02 mg/g, and 66.50 mg/g; those of C1R4 to Pb, Cu, and Cd were 99.80 mg/g, 80.90 mg/g, and 76.54 mg/g. The three adsorbents had different adsorption capacities for different heavy metal ions; the difference between Cu and Cd was more obvious. Under the same dosage, the adsorption capacity of C1R4 was the highest, and that of C4R1 was the lowest. For the same adsorbent, Pb was adsorbed the most, and Cd was adsorbed the least. As the heavy metal concentration increased, 0.05 g of adsorbent could not completely adsorb the heavy metal ions, so the adsorbent dosage for further experiments was 0.10 g.

3.2.2. Impact of pH

When the pH was low, there was a lot of H+, which had an impact on the ion exchange between adsorbent and heavy metals, while heavy metal ions would precipitate when the pH was high [25]. As the pH value of the solution reached 6, Pb would gradually precipitate, and part of it would exist in the form of Pb(OH)2 precipitation; when the pH value was higher than 5, Cu would precipitate in the form of Cu(OH)2 precipitation; and Cd would precipitate when the pH exceeded 8. It can be seen from Figure 7 that when the pH value was lower than 3, the adsorption effects of C4R1, C1R1, and C1R4 on Cu and Cd were all poor. When the pH value reached 6, the equilibrium adsorption capacity tended to balance, and the adsorption capacities of C4R1 to Pb, Cu, and Cd were 49.83 mg/g, 46.5 mg/g, and 46.35 mg/g; those of C1R1 to Pb, Cu, and Cd were 49.83 mg/g, 49.61 mg/g, and 49.36 mg/g; and those of C1R4 to Pb, Cu, and Cd were 49.83 mg/g, 49.70 mg/g, and 49.70 mg/g. Under the same pH condition, the adsorption capacities of C1R4 to Pb, Cu, and Cd were the highest, followed by C1R1, and the lowest was C4R1. When the solution pH was low and the H+ concentration was high, H+ competed with Pb, Cu, and Cd for adsorption, and H+ was more easily ion-exchanged with metal cations inside the adsorbent, occupying a large number of active adsorption sites [33]. As the pH increased, most of the heavy metal ions would be electrostatically adsorbed on the surface of the adsorbent [34], which increased the removal rates of Pb, Cu, and Cd. Meanwhile, the adsorption capacity of three modified composite materials for Pb was stronger than that for Cu and Cd, which might be related to the smallest hydrated ionic radius and the largest atomic weight of Pb. As shown in previous studies [35], Pb2+ and H+ competed more aggressively for active sites on the adsorbent surface in the low pH range, while this phenomenon became less significant as pH increased, so the adsorbents could act stable in a wide pH range for Pb adsorption and had excellent Pb adsorption capacity.

3.2.3. Effect of the Initial Concentration of Pb, Cu, and Cd

In Figure 8, the adsorption capacities of C4R1, C1R1, and C1R4 for Pb, Cu, and Cd steadily rose in the single system as the initial concentration increased, and the amplification curve trends of the adsorbents were basically the same. The adsorption capacity of the adsorbent for the three heavy metals was in the order of Pb > Cu > Cd at any initial concentration. The difference in the adsorption capacities of C4R1, C1R1, and C1R4 was not obvious when the initial concentration was less than 100 mg/L. When the concentration gradually increased from 100 mg/L to 300 mg/L, the difference gradually appeared. When the initial concentration reached 300 mg/L, the equilibrium adsorption capacities of C4R1 for Pb, Cu, and Cd were 148.50 mg/g, 127.01 mg/g, and 124.13 mg/g; those of C1R1 for Pb, Cu, and Cd were 149.81 mg/g, 128.21 mg/g, and 118.98 mg/g; and those of C1R4 for Pb, Cu, and Cd were 149.81 mg/g, 135.96 mg/g, and 127.82 mg/g. The higher equilibrium adsorption capacity indicated that C4R1, C1R1, and C1R4 had better adsorption effects.

3.2.4. Adsorption Isotherms

An isotherm model, which could offer a theoretical foundation for explaining the mechanism of the adsorption process, was one of the most practical and often used methods for modeling adsorption data. The maximum saturation quantity of heavy metal ions adsorbed on the surface of the adsorbent could be calculated using the adsorption isotherm model, and the adsorption capacities of various adsorbents could be compared. The relationship between equilibrium adsorption capacity and equilibrium concentration was shown by the adsorption isotherm curve. The Pb, Cu, and Cd adsorption mechanisms on the modified composite materials were explained by fitting the experimental data using the adsorption isotherm. Three common models, Langmuir [36], Freundlich [37], and Sips [38,39], were used to fit the adsorption data of Pb, Cu, and Cd on C4R1, C1R1, and C1R4, and the isotherm adsorption model suitable for the adsorption process was obtained.
In Figure 9, the adsorption capacities of Pb, Cu, and Cd increased gradually as the initial concentration increased from 0 to 300 mg/L. When the initial concentration was 300 mg/L, the adsorption capacities of C4R1 for Pb, Cu and Cd increased from 141.32 mg/g, 127.51 mg/g and 119.62 mg/g at 25 °C to 145.05 mg/g, 133.59 mg/g and 128.7 mg/g at 45 °C, those of C1R1 for Pb, Cu and Cd increased from 146.72 mg/g, 128.21 mg/g and 120.62 mg/g at 25°C to 147.65 mg/g, 132.39 mg/g, 136.27 mg/g at 45 °C, those of C1R4 for Pb, Cu and Cd increased from 147.02 mg/g, 131.21 mg/g and 124.22 mg/g at 25 °C to 148.35 mg/g, 138.79 mg/g and 131.27 mg/g at 45 °C. The Langmuir equation assumed monolayer adsorption, while the Freundlich equation assumed multi-molecular layer adsorption, and the Sips isotherm combined limited adsorption and inhomogeneous surface adsorption. The premise of the Langmuir equation was that the adsorbent surface was uniform and that there was no interaction between the adsorbent molecules. The isothermal adsorption parameters obtained by solving the isothermal adsorption model are shown in Table S3. At 25 °C, 35 °C, and 45 °C, the R2 values fitted by the Langmuir model were larger than those fitted by the Freundlich and Sips models, so the Langmuir model was more suitable for fitting the experimental data, indicating that the adsorption of Pb, Cu, and Cd by C4R1, C1R1, and C1R4 was monolayer and the adsorption on the surface of C4R1, C1R1, and C1R4 was uniform [40]. According to the maximum saturated adsorption capacities in Table S3, it could be seen that the adsorption capacities of Cu, Pb, and Cu by C4R1, C1R1, and C1R4 were extremely high.

3.2.5. Adsorption Kinetics

As shown in Figure 10, the adsorption capacities of Pb, Cu, and Cd rose quickly during the first 60 min. In the initial adsorption stage, the heavy metals were fully ion exchanged on the surface of the modified composite material, and the reaction was nearly complete at 60 min. In the early adsorption stage, the equilibrium adsorption capacity increased rapidly; this was because the adsorbent provided abundant adsorption sites and the difference between adsorbents and adsorbates was close, which could quickly fix the heavy metal on the surface of the adsorbent. Since the effective adsorption sites on the adsorbent surface gradually diminished as the heavy metal ions in the solution repelled those that had been immobilized on the adsorbent surface, a slower adsorption rate was seen in the later stages [41]. When the adsorption sites were occupied entirely, the adsorption capacity would not increase, and the adsorption maintained a dynamic equilibrium.
When the adsorption time was 5 min, the adsorption capacities of C4R1 for Pb, Cu and Cd were 35.17 mg/g, 26.54 mg/g and 23.25mg/g, and rapidly increased to 49.52 mg/g, 47.82 mg/g and 45.71 mg/g at 90 min; those of C1R1 were 35.50 mg/g, 26.51 mg/g and 24.22 mg/g at 5 min, and rapidly increased to 49.76 mg/g, 48.22 mg/g and 47.35 mg/g at 90 min; those of C1R4 for Pb, Cu and Cd were 37.12 mg/g, 27.24 mg/g and 24.50 mg/g at 5 min, and rapidly increased to 49.92 mg/g, 49.12 mg/g and 48.21 mg/g at 90 min. The adsorption capacities of the three modified composite materials for Pb, Cu, and Cd in the order of C1R4 > C1R1 > C4R1 were close to the maximum saturation at 90 min and were in dynamic equilibrium, which also showed that the adsorption performance of the three modified composite materials was strong.
The pseudo-first-order, pseudo-second-order, and Elovich kinetic models were used to fit the data of the Pb, Cu, and Cd adsorption by the modified composite materials in the single system [42], and it was discovered that the pseudo-second-order kinetic curves had higher R2 values than the pseudo-first-order and Elovich kinetic curves in Table S4. The theoretical maximum saturated adsorption capacity obtained by the pseudo-second-order kinetic model was much closer to the actual one, thus the pseudo-second-order kinetic model could better fit the chemisorption-dominated adsorption process [43] of Pb, Cd, and Cu in water by three modified composite materials.

3.3. Adsorption Analysis in the Ternary System

In the single system, C4R1, C1R1, and C1R4 had good adsorption capacities on Pb, Cu, and Cd in water. However, the actual situation of water pollution was often more complicated; multiple heavy metals coexisted and interfered with each other [44], and competitive adsorption would occur when treated with adsorbent. Therefore, it was also necessary to study the competitive adsorption of C4R1, C1R1, and C1R4 on Pb, Cu, and Cd in water.

3.3.1. Influence of the Dosage of C4R1, C1R1, and C1R4

The adsorbent dosage had a great influence on the competitive adsorption of Pb, Cu, and Cd in the ternary system. In Figure 11, when the dosage was 0.05 g, the competitive equilibrium adsorption capacities of C4R1 for Pb, Cu, and Cd were 92.70 mg/g, 61.92 mg/g, and 38.92 mg/g; those of C1R1 for Pb, Cu, and Cd were 95.48 mg/g, 63.7 mg/g, and 43.04 mg/g; and those of C1R4 for Pb, Cu, and Cd were 96.04 mg/g, 53.2 mg/g, and 44.56 mg/g. In the ternary system, the adsorption capacity of Pb was about twice that of Cd, and the equilibrium adsorption capacity of Cd was reduced by half compared with the single system. There was competitive adsorption between Pb, Cu, and Cd, and their equilibrium adsorption capacities all decreased in the ternary system. Among them, Pb was less affected, Cu and Cd decreased more, and Cd was more obvious. Hence, this relatively obvious competitive adsorption relationship in the ternary system could be described as that the existence of Pb inhibited the adsorption of Cu and Cd, and Cu also had a certain inhibitory effect on Cd adsorption, while the existence of Cu and Cd did not affect Pb adsorption. The adsorption sequence of the three heavy metals on the modified composite materials was Pb > Cu > Cd. When the dosage reached 0.5 g, the competitive equilibrium adsorption capacities of C4R1, C1R1, and C1R4 for Pb, Cu, and Cd all decreased to less than 10 mg/g. The main reason was that when the dosage increased to a certain value, Pb, Cu, and Cd were almost completely removed, and increasing the dosage would not continue to increase the removal rate, resulting in a gradual decrease in the equilibrium adsorption capacity. Under any dosage, the adsorption capacity of C1R4 for Pb, Cu, and Cd was higher than that of C1R1 and C4R1.

3.3.2. Impact of pH

In the ternary system, when the pH value was low, there was no competitive adsorption between heavy metal ions; the more H+ competed with Pb, Cu, and Cd ions for adsorption sites, so the adsorption capacity was low (Figure 12). With the gradual increase of pH, the adsorption capacities of Pb and Cu increased greatly, while the increase of Cd was small because Cd was weaker than Pb and Cu in the competitive adsorption relationship. The competitive adsorption relationship reduced the adsorption capacities of Pb, Cu, and Cd, and the effect on Cd was greater. When the pH value exceeded 5, Cu would precipitate, which affected the adsorption of Pb and Cd by the modified composite materials in the ternary system. Therefore, the solution pH was adjusted to 5 in the ternary system.

3.3.3. Effect of the Initial Concentration and Temperature

In the ternary system, when the initial concentration of Pb, Cu, and Cd was low, competitive adsorption was not obvious in Figure 13. As the initial concentration gradually increased, the amount of Pb, Cu, and Cd that needed to be ion-exchanged increased, and the adsorbent remained constant, so the competitive adsorption was gradually obvious [45]. The priority order of the modified composite materials for heavy metal adsorption is Pb, Cu, and Cd, and the competitive adsorption difference gradually decreased as the proportion of red mud in the modified composite material increased. Meanwhile, the orders of the equilibrium adsorption capacities for three heavy metals were all C1R4 > C1R1 > C4R1, and the adsorption capacities of C1R4 were the strongest. The equilibrium adsorption capacity of Pb, Cu, and Cd increased gradually as the temperature increased from 25 °C to 45 °C (Figure 14). Increasing the temperature would be beneficial to the adsorption reaction because the ionic activity would be improved. At any temperature, the relationship between competitive adsorption and adsorption capacity was Pb > Cu > Cd and C1R4 > C1R1 > C4R1. When the temperature was low, the competitive adsorption of heavy metal ions by C4R1, C1R1, and C1R4 had a large difference, and when the temperature reached 45 °C, the difference became small.

3.3.4. Adsorption Kinetics

In the ternary system, the kinetic adsorption results of Figure 15 showed that the adsorption equilibrium time of C1R4 was faster than that of C1R1 and C4R1, and the equilibrium adsorption capacity of C1R4 was the highest. The time to reach the adsorption equilibrium was 60 min for Pb and 90 min for Cu and Cd. The maximum adsorption capacities of C4R1 for Pb, Cu, and Cd were 45.10 mg/g, 42.20 mg/g, and 33.88 mg/g; those of C1R1 for Pb, Cu, and Cd were 47.80 mg/g, 46.10 mg/g, and 36.11 mg/g; those of C1R4 for Pb, Cu, and Cd were 48.29 mg/g, 47.80 mg/g, and 39.00 mg/g. The adsorption capacity of C1R4 was the largest, and that of C4R1 was the smallest. In the ternary system, the R2 values of the pseudo-second-order kinetic curves were larger than those of the pseudo-first-order and Elovich kinetic curves in Table S5, indicating that the competitive adsorption process of heavy metals in water by modified composite materials was dominated by chemical adsorption.

3.4. Comparison of Single and Ternary Systems

When the temperature was 25 °C, the adsorbent dosage was 0.1 g, the initial heavy metal concentration was 100 mg/L, pH = 6 (single system) or 5 (ternary system), and adsorption time was 90 min, in the single system, the adsorption capacities of C4R1 for Pb, Cu and Cd was 49.90 mg/g, 46.50 mg/g and 46.35 mg/g, those of C1R1 for Pb, Cu and Cd were 49.92 mg/g, 49.36 mg/g and 48.87 mg/g, those of C1R4 for Pb, Cu and Cd were 49.96 mg/g, 49.70 mg/g and 49.61 mg/g; while in the ternary system, the adsorption capacities of C4R1 for Pb, Cu and Cd were 49.66 mg/g, 44.29 mg/g and 33.88 mg/g, those of C1R1 for Pb, Cu and Cd were 49.67 mg/g, 46.57 mg/g and 36.10 mg/g, those of C1R4 for Pb, Cu and Cd were 49.70 mg/g, 47.82 mg/g and 38.20 mg/g. It could be seen that C4R1, C1R1, and C1R4 all had good adsorption effects on Pb, Cu, and Cd in the two systems under the same condition; the adsorption of C4R1, C1R1, and C1R4 for Pb was better than that of Cu and Cd, and C1R4 had the highest adsorption capacity. Kinetic analysis in Table S4 and S5 demonstrated that the pseudo-second-order kinetic equation could better explain the adsorption processes of Pb, Cu, and Cd. The fitting of the Freundlich, Langmuir, and Sips isotherm models in Table S3 indicated that the Langmuir model could better fit the adsorption processes of Pb, Cu, and Cd on C4R1, C1R1, and C1R4, and increasing the temperature could promote the adsorption capacity. The adsorption capacities of C4R1, C1R1, and C1R4 in the ternary system decreased compared with those in the single system, which could demonstrate that there were competitive adsorption relationships among heavy metal ions and that the preferential adsorption order was Pb > Cu > Cd.

4. Conclusions

Modified composite materials were synthesized from CFA and RM mixed and melted in three proportions and then were applied to adsorb Pb, Cu, and Cd in water. The adsorption capacities of C4R1, C1R1, and C1R4 for Pb were the strongest, and those for Cd were the weakest. When the solution pH was nearly neutral, the modified composite materials had a good adsorption effect. By increasing the adsorbent dosage, the valid adsorption sites on the adsorbent surface increased, and the adsorption effect increased. Raising the temperature could also increase the adsorption capacity by increasing the adsorbent activity. The adsorption process was fast, and it generally finished within 90 min. In the single and ternary systems, the adsorption capacity order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. In the ternary system, the preferential adsorption order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. The competition among heavy metal ions was more significant as their initial concentration increased. The pseudo-second-order adsorption kinetic model and Langmuir isotherm model could better fit the adsorption processes.
Modified composite materials had a porous structure and good pore capacity, and the specific surface areas of C4R1, C1R1, and C1R4 were 29.66 m2/g, 32.51 m2/g, and 63.83 m2/g, respectively. As the proportion of RM increased, the specific surface area and adsorption capacity increased, so C1R4 had the strongest adsorption capacity, the largest specific surface area, the largest amounts of pores, and the magnetic property, which was convenient for material recovery and secondary utilization. Through the analysis of physical and chemical properties, the adsorption of Pb, Cu, and Cd by modified composite materials mainly relied on ion exchange, inner sphere complexation, and the electrostatic attraction of the surface hydroxyl groups. The combined use of CFA and RM could solve the problem of solid waste accumulation and create an efficient and economical adsorbent for removing heavy metals from water.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w15040767/s1. Figure S1: Scheme of coal fly ash (CFA)-red mud (RM) modified composite material preparation, performance characterization, and adsorption analysis; Figure S2: Pore size distribution of CFA, RM, C4R1, C1R1, and C1R4; Table S1: Percentage of each element for CFA, RM, C4R1, C1R1, and C1R4 in EDS analysis; Table S2: Physical properties of CFA, RM, C4R1, C1R1, and C1R4; Table S3: Adsorption isothermal parameters of Pb, Cu, and Cd by C4R1, C1R1, and C1R4; Table S4: Kinetic fitting parameters of C4R1, C1R1, and C1R4 in the single system; Table S5: Kinetic fitting parameters of C4R1, C1R1, and C1R4 in the ternary system.

Author Contributions

Conceptualization, H.L. and Y.Z.; methodology, H.L., B.L. and X.T.; software, B.Y. and M.S.; validation, X.T. and B.L.; formal analysis, X.T. and Y.Z.; investigation, H.L., Z.L., M.S. and B.Y.; resources, Y.Z.; data curation, Z.L. and X.T.; writing—original draft preparation, Y.Z. and H.L.; writing—review and editing, X.T.; visualization, B.Y. and H.L.; supervision, X.T.; project administration, Y.Z.; funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Fundamental Research Funds for the Central Universities (451180304165), the Environmental Protection Research Project of Ecology and Environment Department of Jilin Province (No. 2019-12), and the Science and Technology Innovation Project (QDKY202001) of the 7th Institute of Geology & Mineral Exploration of Shandong Province.

Data Availability Statement

Data are contained within the article or Supplementary Material.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Chen, X.; Song, H.; Guo, Y.; Wang, L.; Cheng, F. Converting waste coal fly ash into effective adsorbent for the removal of ammonia nitrogen in water. J. Mater. Sci. 2018, 53, 12731–12740. [Google Scholar] [CrossRef]
  2. Gautam, R.K.; Sharma, S.K.; Mahiya, S.; Chattopadhyaya, M.C. CHAPTER 1. Contamination of Heavy Metals in Aquatic Media: Transport, Toxicity and Technologies for Remediation. In Heavy Metals in Water; Royal Society of Chemistry: Cambridge, UK, 2014; pp. 1–24. [Google Scholar]
  3. Shang, Z.; Zhang, L.; Zhao, X.; Liu, S.; Li, D. Removal of Pb(II), Cd(II) and Hg(II) from aqueous solution by mercapto-modified coal gangue. J. Environ. Manag. 2019, 231, 391–396. [Google Scholar] [CrossRef] [PubMed]
  4. Bilal, M.; Ihsanullah, I.; Ul Hassan Shah, M.; Younas, M. Enhanced removal of cadmium from water using bio-sorbents synthesized from branches and leaves of Capparis decidua and Ziziphus mauritiana. Environ. Technol. Innov. 2021, 24, 101922. [Google Scholar] [CrossRef]
  5. Huang, H.; Liu, J.; Ding, L. Recovery of phosphate and ammonia nitrogen from the anaerobic digestion supernatant of activated sludge by chemical precipitation. J. Clean. Prod. 2015, 102, 437–446. [Google Scholar] [CrossRef]
  6. Meng, X.; Khoso, S.A.; Jiang, F.; Zhang, Y.; Yue, T.; Gao, J.; Lin, S.; Liu, R.; Gao, Z.; Chen, P.; et al. Removal of chemical oxygen demand and ammonia nitrogen from lead smelting wastewater with high salts content using electrochemical oxidation combined with coagulation–flocculation treatment. Sep. Purif. Technol. 2020, 235, 116233. [Google Scholar] [CrossRef]
  7. Verma, R.; Sarkar, S. Trace Cr(VI) Removal: Evidence of Redox-Active Ion Exchange by a Weak-Base Anion Exchanger. Ind. Eng. Chem. Res. 2020, 59, 21187–21195. [Google Scholar] [CrossRef]
  8. Adam, M.R.; Othman, M.H.D.; Abu Samah, R.; Puteh, M.H.; Ismail, A.F.; Mustafa, A.; Rahman, M.A.; Jaafar, J. Current trends and future prospects of ammonia removal in wastewater: A comprehensive review on adsorptive membrane development. Sep. Purif. Technol. 2019, 213, 114–132. [Google Scholar] [CrossRef]
  9. Zhang, H.; Wang, X.; Li, N.; Xia, J.; Meng, Q.; Ding, J.; Lu, J. Synthesis and characterization of TiO2/graphene oxide nanocomposites for photoreduction of heavy metal ions in reverse osmosis concentrate. RSC Adv. 2018, 8, 34241–34251. [Google Scholar] [CrossRef] [Green Version]
  10. Wang, S.; Peng, Y. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J. 2010, 156, 11–24. [Google Scholar] [CrossRef]
  11. Shi, Q.; Sterbinsky, G.E.; Prigiobbe, V.; Meng, X. Mechanistic Study of Lead Adsorption on Activated Carbon. Langmuir 2018, 34, 13565–13573. [Google Scholar] [CrossRef]
  12. Sipos, P.; Kis, V.K.; Balázs, R.; Tóth, A.; Németh, T. Effect of pedogenic iron-oxyhydroxide removal on the metal sorption by soil clay minerals. J. Soil Sediment 2021, 21, 1785–1799. [Google Scholar] [CrossRef]
  13. Morosanu, I.; Teodosiu, C.; Paduraru, C.; Ibanescu, D.; Tofan, L. Biosorption of lead ions from aqueous effluents by rapeseed biomass. New Biotechnol. 2017, 39, 110–124. [Google Scholar] [CrossRef] [PubMed]
  14. Yurak, V.; Apakashev, R.; Dushin, A.; Usmanov, A.; Lebzin, M.; Malyshev, A. Testing of Natural Sorbents for the Assessment of Heavy Metal Ions’ Adsorption. Appl. Sci. 2021, 11, 3723. [Google Scholar] [CrossRef]
  15. Wang, P.; Liu, D.-Y. Physical and Chemical Properties of Sintering Red Mud and Bayer Red Mud and the Implications for Beneficial Utilization. Materials 2012, 5, 1800–1810. [Google Scholar] [CrossRef] [Green Version]
  16. Wang, S.; Wu, H. Environmental-benign utilisation of fly ash as low-cost adsorbents. J. Hazard. Mater. 2006, 136, 482–501. [Google Scholar] [CrossRef]
  17. Pang, Y.; Zhao, C.; Li, Y.; Li, Q.; Bayongzhong, X.; Peng, D.; Huang, T. Cadmium adsorption performance and mechanism from aqueous solution using red mud modified with amorphous MnO2. Sci. Rep. 2022, 12, 4424. [Google Scholar] [CrossRef]
  18. Du, Y.; Dai, M.; Cao, J.; Peng, C. Fabrication of a low-cost adsorbent supported zero-valent iron by using red mud for removing Pb(ii) and Cr(vi) from aqueous solutions. RSC Adv. 2019, 9, 33486–33496. [Google Scholar] [CrossRef] [Green Version]
  19. Bai, B.; Bai, F.; Li, X.; Nie, Q.; Jia, X.; Wu, H. The remediation efficiency of heavy metal pollutants in water by industrial red mud particle waste. Environ. Technol. Innov. 2022, 28, 102944. [Google Scholar] [CrossRef]
  20. Huang, X.; Zhao, H.; Zhang, G.; Li, J.; Yang, Y.; Ji, P. Potential of removing Cd(II) and Pb(II) from contaminated water using a newly modified fly ash. Chemosphere 2020, 242, 125148. [Google Scholar] [CrossRef]
  21. Wen, W.; Jia, L.; Xie, J.; Zhao, W.; Feng, H.; Cao, D.; Sun, F.; Han, P.; Bai, X.; He, B. Electrochemical response of solidification Cu2+ contaminated soil influenced by red mud/fly ash ratio. Heliyon 2022, 8, e10971. [Google Scholar] [CrossRef]
  22. Li, Y.; Min, X.; Ke, Y.; Liu, D.; Tang, C. Preparation of red mud-based geopolymer materials from MSWI fly ash and red mud by mechanical activation. Waste Manag. 2019, 83, 202–208. [Google Scholar] [CrossRef] [PubMed]
  23. Adra, A.; Morin, G.; Ona-Nguema, G.; Brest, J. Arsenate and arsenite adsorption onto Al-containing ferrihydrites. Implications for arsenic immobilization after neutralization of acid mine drainage. Appl. Geochem. 2016, 64, 2–9. [Google Scholar] [CrossRef]
  24. Buema, G.; Harja, M.; Lupu, N.; Chiriac, H.; Forminte, L.; Ciobanu, G.; Bucur, D.; Bucur, R.D. Adsorption Performance of Modified Fly Ash for Copper Ion Removal from Aqueous Solution. Water 2021, 13, 207. [Google Scholar] [CrossRef]
  25. Luu, T.-T.; Dinh, V.-P.; Nguyen, Q.-H.; Tran, N.-Q.; Nguyen, D.-K.; Ho, T.-H.; Nguyen, V.-D.; Tran, D.X.; Kiet, H.A.T. Pb(II) adsorption mechanism and capability from aqueous solution using red mud modified by chitosan. Chemosphere 2022, 287, 132279. [Google Scholar] [CrossRef]
  26. Xue, Q.; Li, J.-S.; Wang, P.; Liu, L.; Li, Z.-Z. Removal of Heavy Metals from Landfill Leachate Using Municipal Solid Waste Incineration Fly Ash as Adsorbent. CLEAN-Soil Air Water 2014, 42, 1626–1631. [Google Scholar] [CrossRef]
  27. Lyu, F.; Niu, S.; Wang, L.; Liu, R.; Sun, W.; He, D. Efficient removal of Pb(II) ions from aqueous solution by modified red mud. J. Hazard. Mater. 2021, 406, 124678. [Google Scholar] [CrossRef]
  28. Wang, L.; Huang, X.; Zhang, J.; Wu, F.; Liu, F.; Zhao, H.; Hu, X.; Zhao, X.; Li, J.; Ju, X.; et al. Stabilization of lead in waste water and farmland soil using modified coal fly ash. J. Clean. Prod. 2021, 314, 127957. [Google Scholar] [CrossRef]
  29. Nguyen, T.C.; Tran, T.D.M.; Dao, V.B.; Vu, Q.-T.; Nguyen, T.D.; Thai, H. Using Modified Fly Ash for Removal of Heavy Metal Ions from Aqueous Solution. J. Chem. 2020, 2020, 8428473. [Google Scholar] [CrossRef]
  30. Guo, R.; Yao, W.; Ma, H.; Yuan, J. Two-step hydrothermal synthesis of nano-kaolinite from fly ash: Thermodynamics and mechanism. J. Clean. Prod. 2020, 271, 122567. [Google Scholar] [CrossRef]
  31. Lakshmi Narayanan, S.; Venkatesan, G.; Vetha Potheher, I. Equilibrium studies on removal of lead (II) ions from aqueous solution by adsorption using modified red mud. Int. J. Environ. Sci. Technol. 2017, 15, 1687–1698. [Google Scholar] [CrossRef]
  32. Jiang, X.; Fan, W.; Li, C.; Wang, Y.; Bai, J.; Yang, H.; Liu, X. Removal of Cr(vi) from wastewater by a two-step method of oxalic acid reduction-modified fly ash adsorption. RSC Adv. 2019, 9, 33949–33956. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  33. Yang, T.; Wang, Y.; Sheng, L.; He, C.; Sun, W.; He, Q. Enhancing Cd(II) sorption by red mud with heat treatment: Performance and mechanisms of sorption. J. Environ. Manag. 2020, 255, 109866. [Google Scholar] [CrossRef] [PubMed]
  34. Zhou, C.; Wang, X.; Wang, Y.; Song, X.; Fang, D.; Ge, S. The sorption of single- and multi-heavy metals in aqueous solution using enhanced nano-hydroxyapatite assisted with ultrasonic. J. Environ. Chem. Eng. 2021, 9, 105240. [Google Scholar] [CrossRef]
  35. Carvalheiras, J.; Novais, R.M.; Labrincha, J.A. Metakaolin/red mud-derived geopolymer monoliths: Novel bulk-type sorbents for lead removal from wastewaters. Appl. Clay Sci. 2023, 232, 106770. [Google Scholar] [CrossRef]
  36. Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361–1403. [Google Scholar] [CrossRef] [Green Version]
  37. Freundlich, H.M.F. Over the Adsorption in Solution. J. Phys. Chem. 1906, 57, 385–470. [Google Scholar]
  38. Sips, R. On the Structure of a Catalyst Surface. J. Chem. Phys. 1948, 16, 490–495. [Google Scholar] [CrossRef]
  39. Sips, R. On the structure of a catalyst surface. II. J. Chem. Phys. 1950, 18, 1024–1026. [Google Scholar] [CrossRef]
  40. Sun, L.; Chen, D.; Wan, S.; Yu, Z. Performance, kinetics, and equilibrium of methylene blue adsorption on biochar derived from eucalyptus saw dust modified with citric, tartaric, and acetic acids. Bioresour. Technol. 2015, 198, 300–308. [Google Scholar] [CrossRef]
  41. Liu, Y.; Chen, M.; Yongmei, H. Study on the adsorption of Cu(II) by EDTA functionalized Fe3O4 magnetic nano-particles. Chem. Eng. J. 2013, 218, 46–54. [Google Scholar] [CrossRef]
  42. Simonin, J.-P. On the comparison of pseudo-first order and pseudo-second order rate laws in the modeling of adsorption kinetics. Chem. Eng. J. 2016, 300, 254–263. [Google Scholar] [CrossRef]
  43. Gao, X.; Guo, C.; Hao, J.; Zhao, Z.; Long, H.; Li, M. Adsorption of heavy metal ions by sodium alginate based adsorbent-a review and new perspectives. Int. J. Biol. Macromol. 2020, 164, 4423–4434. [Google Scholar] [CrossRef] [PubMed]
  44. Wang, R.; Shafi, M.; Ma, J.; Zhong, B.; Guo, J.; Hu, X.; Xu, W.; Yang, Y.; Ruan, Z.; Wang, Y.; et al. Effect of amendments on contaminated soil of multiple heavy metals and accumulation of heavy metals in plants. Environ. Sci. Pollut. Res. Int. 2018, 25, 28695–28704. [Google Scholar] [CrossRef] [PubMed]
  45. Park, J.H.; Ok, Y.S.; Kim, S.H.; Cho, J.S.; Heo, J.S.; Delaune, R.D.; Seo, D.C. Competitive adsorption of heavy metals onto sesame straw biochar in aqueous solutions. Chemosphere 2016, 142, 77–83. [Google Scholar] [CrossRef]
Water 15 00767 g001 550
Figure 1. SEM spectra of (a) CFA, (b) RM, (c) C4R1, (d) C1R1, and (e) C1R4.
Figure 1. SEM spectra of (a) CFA, (b) RM, (c) C4R1, (d) C1R1, and (e) C1R4.
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Figure 2. Energy spectra of (a) CFA, (b) RM, (c) C4R1, (d) C1R1, and (e) C1R4.
Figure 2. Energy spectra of (a) CFA, (b) RM, (c) C4R1, (d) C1R1, and (e) C1R4.
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Figure 3. Relative quantity adsorbed of (a) CFA and RM, (b) C4R1, C1R1, and C1R4.
Figure 3. Relative quantity adsorbed of (a) CFA and RM, (b) C4R1, C1R1, and C1R4.
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Figure 4. FTIR spectra of (a) CFA, (b) RM, (c) C4R1, C1R1, and C1R4.
Figure 4. FTIR spectra of (a) CFA, (b) RM, (c) C4R1, C1R1, and C1R4.
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Figure 5. Hysteresis curves of (a) CFA, (b) RM, (c) C4R1, C1R1, and C1R4.
Figure 5. Hysteresis curves of (a) CFA, (b) RM, (c) C4R1, C1R1, and C1R4.
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Figure 6. Effect of the dosage of (a) C4R1, (b) C1R1, and (c) C1R4 on Pb, Cu, and Cd adsorption in the single system.
Figure 6. Effect of the dosage of (a) C4R1, (b) C1R1, and (c) C1R4 on Pb, Cu, and Cd adsorption in the single system.
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Figure 7. Influence of pH on the adsorption of Pb, Cu, and Cd by (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
Figure 7. Influence of pH on the adsorption of Pb, Cu, and Cd by (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
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Figure 8. Effect of initial heavy metal concentration on adsorption capacities of (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
Figure 8. Effect of initial heavy metal concentration on adsorption capacities of (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
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Figure 9. Adsorption isotherms of (a) Pb on C4R1, (b) Cu on C4R1, (c) Cd on C4R1, (d) Pb on C1R1, (e) Cu on C1R1, (f) Cd on C1R1, (g) Pb on C1R4, (h) Cu on C1R4, and (i) Cd on C1R4 in the single system.
Figure 9. Adsorption isotherms of (a) Pb on C4R1, (b) Cu on C4R1, (c) Cd on C4R1, (d) Pb on C1R1, (e) Cu on C1R1, (f) Cd on C1R1, (g) Pb on C1R4, (h) Cu on C1R4, and (i) Cd on C1R4 in the single system.
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Figure 10. Kinetic fitting of (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
Figure 10. Kinetic fitting of (a) C4R1, (b) C1R1, and (c) C1R4 in the single system.
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Figure 11. Impact of the dosage of (a) C4R1, (b) C1R1, and (c) C1R4 on Pb, Cu, and Cd adsorption in the ternary system.
Figure 11. Impact of the dosage of (a) C4R1, (b) C1R1, and (c) C1R4 on Pb, Cu, and Cd adsorption in the ternary system.
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Figure 12. Influence of pH on the adsorption of Pb, Cu, and Cd by (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
Figure 12. Influence of pH on the adsorption of Pb, Cu, and Cd by (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
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Figure 13. Impact of the initial concentration of heavy metal ions on adsorption capacity of (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
Figure 13. Impact of the initial concentration of heavy metal ions on adsorption capacity of (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
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Figure 14. Effect of temperature on adsorption capacity in the ternary system.
Figure 14. Effect of temperature on adsorption capacity in the ternary system.
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Figure 15. Kinetic fitting of (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
Figure 15. Kinetic fitting of (a) C4R1, (b) C1R1, and (c) C1R4 in the ternary system.
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Zhao, Y.; Luan, H.; Yang, B.; Li, Z.; Song, M.; Li, B.; Tang, X. Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism. Water 2023, 15, 767. https://doi.org/10.3390/w15040767

AMA Style

Zhao Y, Luan H, Yang B, Li Z, Song M, Li B, Tang X. Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism. Water. 2023; 15(4):767. https://doi.org/10.3390/w15040767

Chicago/Turabian Style

Zhao, Yuyan, Hanwen Luan, Binghan Yang, Zhenghe Li, Meitong Song, Bing Li, and Xiaodan Tang. 2023. "Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism" Water 15, no. 4: 767. https://doi.org/10.3390/w15040767

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