Formation of CoAl layered double hydroxide on the boehmite surface and its role in tungstate sorption

Treatment of gold ore cyanidation wastewater by adsorption onto a Hydrotalcite-type anionic clay as a novel adsorbent

The treatment of cyanide contaminated wastewater from a gold processing plant was performed by the synthesized nanostructured Layered Double Hydroxide (LDH) which has known as a Hydrotalcite-type anionic clay. LDH was synthesized by the co-precipitation process, characterized by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), scanning electron microscope (SEM) Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR) and Wavelength Dispersive X-ray analysis (WDX) and applied for removal of free cyanide from both synthetic solution and mining effluent. The maximum particle size of synthesized LDH was determined to be 4 nm based on the Scherrer's equation. The maximum loading capacity of LDH, 60 mg/g, indicates that LDH is an interesting adsorbent for cyanide removal. The data modeling showed that the kinetic and equilibrium data best fitted by FPKM and RPIM, respectively, also, rate-controlling step in the adsorption process is intra-particle diffusion based on Weber-Morris plot, and the adsorption of CN^- onto LDH is a two-step process. The thermodynamic studies confirm that the adsorption of free cyanide on Mg/Al LDH is a spontaneous and endothermic process. The energy of activation for adsorption of free cyanide on Mg/Al LDH was determined to be 6.14 kJ/mol, which is in the range physicochemical sorption. The mining wastewater treatment was performed by the synthesized LDH. The adsorption experiments showed that more than 90% of free cyanide was removed from the real solution during a short period of contact time, which confirms the ability of LDH for the treatment of industrial cyanide contaminated wastewater. Graphical abstract.

Sorption of Molybdates and Tungstates on Functionalized Montmorillonites: Structural and Textural Features

Montmorillonite—the most popular mineral of the smectite group—has been recognized as a low-cost, easily available mineral sorbent of heavy metals and other organic and inorganic compounds that pollute water. The aim of this work was to determine the sorption mechanism and to identify the reaction products formed on the surface of montmorillonite and organo-montmorillonite after sorption of molybdates (Mo(VI)) and tungstates (W(VI)). Montmorillonites are often modified to generate a negative charge on the surface. The main objective of the study was to investigate and compare the features of Na-montmorillonite (Na-M), montmorillonite modified with dodecyl trimethyl ammonium bromide (DDTMA-M), and montmorillonite modified with didodecyl dimethyl ammonium bromide (DDDDMA-M) before and after sorption experiments. The material obtained after sorption was studied by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The XRD pattern showed the presence of a new crystallic phase in the sample that was observed under an SEM as an accumulation of crystals. The FTIR spectra showed bands related to Mo–O and W–O vibration (840 and 940 cm⁻¹, respectively). The obtained results suggest that molybdenum(VI) and tungsten(VI) ions sorb onto the organo-montmorillonite in the form of alkylammonium molybdates and tungstates.