The paper deals with the feasibility of arsenite removal by the adsorption from bentonite mineral. Groundwater arsenic contamination has been reported in different parts of the world including Jharkhand, Bihar and Uttar Pradesh. Tube wells in Holocene Newer Alluvium are characterized by grey to black coloured organic-rich argillaceous sediments which have arsenic-contaminated groundwater. The majority of arsenic present in the groundwater is in the form of As(III) which exists as uncharged species arsenic tri hydroxide at pH value of less than 9.2. Arsenite is removed by various techniques like coagulation microfiltration, fixed bed adsorption, bioremoval, ion exchange, membrane filtration, etc. Our studies have shown that locally available bentonites containing a unit of montmorillonites can remove the arsenic from an aqueous medium. On the treatment of 100 mL arsenite solution with 300 mesh sieves bentonites up to different intervals of time, it has been found that bentonites are good adsorbent of arsenite. The percentage removal of arsenite is up to 99 per cent with 3 g sodium derivative of bentonite for 1 hour. The removal efficiency, adsorption isotherm and kinetic studies show the suitability of bentonite minerals for arsenic removal following first-order kinetics. Freundlich and Langmuir isotherms are obeyed in the adsorption of arsenite by bentonite minerals. Adsorption of arsenic by bentonite minerals has proved to be a low-cost eco-friendly method. Sodium derivative of bentonite minerals has been found more efficient for removal of arsenite.

In this study, the chemical co-precipitation method was used to prepare magnetic nano-Fe3O4. In order to investigate the adsorption capacity of magnetic nano-Fe3O4 for Cr(VI) in aqueous solution, three aspects of solution pH, magnetic nano-Fe3O4 dosage and initial solution concentration were studied. The experimental results showed that Cr(VI) adsorption capacity by magnetic nano-Fe3O4 decreased with increasing pH and increased with the increasing initial concentration of Cr(VI) ions and magnetic nano-Fe3O4 dosage. In addition, the experimental data were fitted to the adsorption kinetics and three adsorption isotherms. It could be seen that the adsorption process of Cr(VI) by magnetic nano-Fe3O4 accorded with pseudo-second-order kinetics, which demonstrated that the adsorption process was controlled by chemical adsorption. And it was also found to be well represented by the Freundlich isotherm model. The maximum capacity obtained from the Langmuir model was 34.0136 mg/g, indicating that magnetic nano-Fe3O4 is an efficient adsorbent.