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The presence of arsenic in base metal concentrates including copper, lead, and zinc creates problems such as low quality of final product and environmental issues. Therefore, additional processing steps for removing arsenic are required. Among several methods to reduce arsenic from these concentrates, alkaline leaching was selected as an efficient and simple method. In this research, sodium sulfide and sodium hydroxide mixtures were used for arsenic elimination from lead concentrate produced by Zarrin Madan Asia Company. To obtain optimum conditions, the effect of some parameters such as temperature, leaching time, liquid/solid ratio (L/S), sodium sulfide, and sodium hydroxide concentrations on arsenic removal was investigated. Based on characterization methods, mimetite was the main arsenic compound in lead concentrate; however, after alkaline sulfide leaching, the starting material was decomposed, and lead was mainly transformed to PbS. Accordingly, up to 98% of arsenic was removed under optimum selective leaching conditions (30 g/L of sulfide sodium, 5 g/L of sodium hydroxide, at 85 °C, 15 min, and L/S ratio = 7). To immobilize arsenic from alkaline leaching, the precipitation method was used by finding optimum conditions (at Fe/As = 3, 25 °C and 12 h). Therefore, the final product was suitable for further smelting processes without any environmental problems.

The purpose of this study is to develop the kinetic model and to find the optimum leaching conditions for maximum alumina dissolution from sintered nepheline syenite resource in the alkaline solution. About 80% of alumina (smaller than 5% of silica) was effectively recovered at 80 °C, 3 M NaOH, particle size less than 88 μm, agitation speed of 800 rpm, and leaching time of 60 min with a minimum amount of silica dissolution. Based on the kinetic model and the obtained reaction degree of each effective parameter, the experimental data were simulated. The simulation results proved that the leaching process for alumina was controlled by diffusion through the solid product layer and reaction at the interface of unreacted core that was confirmed by the value of activation energy (15.53 kJ/mol). The provided optimum conditions could be effective to decrease the silica dissolution, and to improve the alumina recovery.

The polythermal crystallization method has been used to extract sodium and potassium carbonate salts as valuable by-products. The salt production was carried out using an alkaline carbonate solutio...

Arsenic removal has received much attention all over the world because of its toxicity and carcinogenicity. In the current research, the adsorption behavior of As(V) from aqueous solution onto Fe(III)-impregnated bentonite (Fe-Bent) was examined. Adsorption experiment results showed that the adsorption capacity of initial bentonite clay (Bent) was increased by Fe(III)-impregnation method. In Fe-Bent, the mononuclear Fe(III) cations, small oligomeric cluster and bulky FexOy particles were made such active sites identified by UV–Vis spectroscopy. X-ray diffraction results showed that Fe(III) species presented mainly in both crystalline and amorphous forms on the external surface of Fe-Bent. In an experimental study, the effect of different parameters such as contact times, arsenic concentrations, adsorbent dosages, pH and temperature conditions was investigated. Fe-Bent sample represented the maximum adsorption capacity of 10.06 mg L−1 to remove 5–20 mg L−1 of As(V) at pH = 6 and ambient temperature. In this experiment, the residual As(V) concentration decreased to less than 0.01 mg/L with the adsorption efficiency of 99% (i.e., below the limit of the WHO). The two- and three-parameter isotherm models revealed the best fit to the Freundlich, Sips, Toth, Temkin and Langmuir models, respectively. The isotherm models indicated the strong adsorption between arsenic and Fe-Bent. The adsorption kinetics was also considered by first-order, second-order and Elovich rate equations. It was noticed that the Fe-Bent adsorption followed the external surface reaction such as ligand exchange and surface complexation. The thermodynamics studies exposed that the process was spontaneous and endothermic for Fe-Bent.

Bentonite clays containing mostly montmorillonite as a nanostructure group of smectite have been used as industrial raw material in many applications. The presence of the other impurities in bentonite clays reduces the value of bentonite. Therefore, the bentonite purification is necessary. In this research, the purification and separation of montmorillonite from a low-grade natural bentonite were considered on the regular and comprehensive plan. For this purpose, a set of methods including dispersion, sodium-activation, sedimentation, sonication and centrifugation were used. In contrast to many methods, there were often complex, expensive and non-effective; this purification method was found to be effective for removing almost all quartz, carbonates and clinoptilolite as the major impurities. In this purification method, the montmorillonite content was increased from 15 to 84% with the separation yield of 80%. The influence of centrifugal force and the type of ultrasonication indicated the most critical parameters in the purification yield, the physical properties and the crystalline structure of the final products. The laser particle size distribution analysis, X-ray diffraction, semi-quantitative analysis and Fourier-transform infrared spectroscopy results showed the decrease of impure phase without any structural changes or damages in clay framework.

The present research is focused on the textural, structural and surface properties of Al, Fe and Si hierarchical porous nano-bentonite heterostructure (PBH) derivated from Al, Fe pillared nano-bentonite (Al, Fe-PILB). The application of Al, Fe-PILB as a precursor to prepare porous clay minimized the use of cationic surfactant, water consumption, synthetic time and organic wastes. Furthermore, the incorporation of Al and Fe species from Al, Fe-PILB in the silica framework was performed in one step reaction compared to the conventional method required the continuous control for hydrolysis and condensation in the synthesize of PBH. Besides using Al, Fe-PILB as a precursor, the ultrasonic and microwave techniques were firstly assisted to the synthesis of PBH for opening bentonite layers with breaking pillars resulted in the increasing basal spacing and improving mesoporous silica formation in interlayer space of Al, Fe-PILB in little synthetic time. The LPSD, XRD, UV–Vis spectra, N2 adsorption-desorption, FESEM-EDS, TEM, and FTIR analyses allowed for a better understanding of PBH behaviors under different synthetic conditions. The results showed that the use of pillared clays in the conventional method did not lead to the formation of PBH due to the strong interaction between the Al, Fe species and the clay layers. The synergism effect of ultrasonic waves and microwave irradiation reduced the structural damage of nano-bentonite and improved BET surface area (867 m2/g), micropore and mesopore volume (0.62 cm3/g) compared to the only application of ultrasonic or microwave techniques. These properties make PBH as an attractive candidate for catalysis and adsorption applications.

This review discusses the recent trends in the research over the last 30 years to use clay minerals in natural and modified forms for removing different toxic organic/inorganic pollutants. The natural and modified forms of clay minerals have an exceptional ability to remove different contaminants. However, the modification methods can improve the clay mineral adsorption properties that consequently increase more adsorption sites and functional groups to adsorb different environmental pollutants. This review shows the importance of modification methods and more extension of novel clay preparation based on nanotechnology which could raise the control of pollution. The syntheses of functionalized clays such as pillared clays and porous clay heterostructures introduce the new class of heterostructure materials with high adsorption capacity, capability, and selectivity. Due to the acceptable properties of heterostructure materials including high specific surface area, thermal and mechanical stability, and the existence of multifunctional groups to selective adsorption, this review collects more literature of research related to environmental protection issues. However, it is expected much attention to get a better understanding of the adsorption mechanism, regeneration, and recovery process of these materials.

The elevated contamination of arsenic species emitted from gold mine activities causes serious environmental problems. The modification of natural bentonite clay to obtain the adsorbent with high porosity, large surface area, and high adsorption capacity creates a new group of porous and heterostructure materials for immobilization of arsenic species from gold mine wastewater under alkaline condition, owing to the gold cyanidation process. There is a limited approach in alkaline mine wastewater, because of the negative surface charge of most adsorbents. In this research, the adsorbability of arsenic under synthetic and real alkaline wastewater was investigated for the first time. The Visual MINTEQ geochemical modeling software was applied to simulate the arsenic species under different pH, temperature and co-existing ions in mine wastewater obtained from dewatering unit in Zarshuran gold mine. Optimized parameters and better adsorbent were initially determined from synthetic alkaline wastewater, then the efficiency of the adsorption process in real alkaline mine wastewater was measured. In real wastewater treatment, the obtained adsorption efficiency higher than 70% with high reusability in the alkaline condition is an appropriated for only one step process. The major mechanism for adsorption was chemical with complexation in rapid and slow diffusion into the active sites.

In this paper, the physicochemical properties of natural, pillared and porous nano bentonite heterostructure in the points of view of surface protonation–deprotonation behaviors were studied. Moreover, the structural heterogeneity in each sample based on three-dimensional field-emission scanning electron microscopy (FESEM) plots were investigated to obtain its effect on the formation of surface active sites. To better understand the surface protonation properties and adsorptive capability of natural, pillared and porous clays, it is essential to investigate the surface charge, surface active sites, pH at point of zero charge (pHzpc), and surface acid-base equilibrium constants. Since the information about amphoteric acid-base groups especially in porous clays is still lacking, our main purpose is to obtain the best estimates to compare the surface properties of natural, pillared and porous clays by means of Gran method and surface complexation model from titration data. The 2 pK-diffusion layer model (DLM) was applied to evaluate the contribution and concentration of the various surface site species (such as SOH, SOH2+, and SO−) in the different pH and ionic strengths. This paper indicates considerable new information about surface acid-base reactions, total surface site concentrations, pHzpc measurement, which provides basic knowledge of the underlying adsorption mechanisms. The maximum value of total surface sites concentration (8.84 mmol/L) in ionic strengths of 0.05 M NaCl belonged to porous nano bentonite heterostructure (PBH) with the highest pHzpc at 9.73.

To improve adsorption mechanism and to increase adsorption capability for Na-bentonite rather than Ca-bentonite origin, Nano-bentonite sample with Na activation was used. Also for investigation of environmental effect, some parameters such as pH, adsorbent concentration, metal ion concentration and stirrer speed on the adsorption rate of Zn used Experimental Design software and Central Composite Design (CCD) model. CCD is a powerful model that based on minimization of errors and exprement repeat. This model usually was used when there aren’t suitable knowledge about investigating factors or their borderline. In this research 30 experiments were designed for Na-Bentonite samples and the effective parameters on Zn adsoption rate were denoted by CCD model analysis results. Based on obtained results, pH and adsorbent concentration introduced as the most effective parameters. The pH and metal ion concentration is only valid interaction effect on recovery of metal ion adsorption. Finally, the optimized condition of each parameter for effective adsoption process was determined and possible conditions for access to adsorption recovery up to 99 percent was prepared.