FAU—Type Zeolite Synthesis from Clays and Its Use for the Simultaneous Adsorption of Five Divalent Metals from Aqueous Solutions

In this research, a vermiculite-kaolinite clay (VK) was used to prepare faujasite zeolites via alkaline fusion and hydrothermal crystallisation. The optimal synthesis conditions were 1 h fusion with NaOH at 800 °C, addition of deionised water to the fused sample at a sample to deionised water mass ratio of 1:5, 68 h of non-agitated ageing of the suspension, and 24 h of hydrothermal treatment at 90 °C. The efficacy of the prepared faujasite was compared to raw clay and a reference zeolite material through adsorption experiments of aqueous solutions containing five divalent cations—Cd, Co, Cu, Pb, and Zn. The results showed that in the presence of competing cations at concentrations of 300 mg L−1 and adsorbent loading of 5 g L−1, within the first 10 min, about 99% of Pb, 60% of Cu, 58% of Cd, 28% of Zn, and 19% of Co were removed by the faujasite prepared from clay. Two to four parameter nonlinear adsorption isotherms were used to fit the adsorption data and it was found that overall, three and four parameter isotherms had the best fit for the adsorption process.

Study of interactions between rhodamine B and a beidellite-rich clay fraction

The interaction between a basic dye, rhodamine B, and a separated fine fraction from natural clay was studied. Chemical analysis, X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the predominance of beidellite in the fine clay fraction. The interaction of rhodamine B with the fine clay fraction showed that sorption was fast and followed a pseudo-second-order kinetic model. The comparison between sorbed rhodamine B amounts as a function of the various experimental parameters such as pH, sorbent mass, dye concentration and the presence of competing ions suggests that: (1) the sorption process is largely pH-dependent; (2) significant competition is observed between the dye and the Ca2+ and Mg2+ ions; (3) the sorption proceeds, principally, by a cation-exchange mechanism; and (4) the sorption capacity of the fine fraction in the presence of competing cations such as Ca2+ is ~0.28 mmol g–1.

Cladophora sp. Biosorption of Metal-contaminated Water

Artisanal and Small-scale Gold Mining (ASGM) activities employing the mercury amal-gamationtechnique have resulted in a significant drop in the quality of water from Ngwabalozi River, Zimbabwe. Mercury levels as high as 0.31 mg L-1have been reported in its waters and the low river pH (pH 3) favors proliferation of microorganisms responsible for methylmercury (a potent neurotoxin) formation. Thus, removal of mercury from contaminated systems is a priority. Therefore, the aim of this study is to develop a low-cost batch reactor for the removal of mercury from mercury contaminated acidic waters tomeet the World Health Organization (WHO) standard of 0.006 mg L-1using Cladophorasp. algae. Optimum reactor parameters were deter-mined by studying the effect of contact time, pH, initial mercury concentration and the presence of competing cations on the adsorption of mercury by Cladophorasp. The mass of algae required in a 1000 Lbatch reactor was then determined at the optimum adsorption conditions for the single and multi-component solution systems. A rapid uptake of mercury by Cladophorasp. algae was displayed. More than 99% of the mercury in solution was removed within the first five minutes of contact and equilibrium was attained after ten minutes. High adsorption capacities (up to 805 mg kg-1at pH 3) were obtained at the optimum mercury concentration of 1.0 mg L-1. Competitive adsorption studies showed that the selectivity of cations by Cladophora sp. was in thefollowing order: Hg2+˃ Fe2+˃ Cu2+˃ Zn2+˃ Co2+. Based on the optimized reactor conditions, nearly 4.8 kg of Cladophorasp. per 1000 Lbatch is required to treat the water in Ngwabalozi River for a mercury only solution. However, for a multi-component system, the mass of Cladophorasp. required was more than triple (17.1 kg) the mass required in a single component solution.