Removal of Cr(VI) from wastewater by anionic clays

Wastes containing chromium are considered hazardous because of their behavior in the deep soil layers when stored in landfills. In an alkaline medium, it is estimated that the stability of chromate can be 50 years; they can migrate to groundwater, even through cohesive soils. That is why we are interested in the elimination of chromium VI by a strong adsorbent such as one that belongs to the family of layered double hydroxides (anionic clays). These materials are synthesized by co-precipitation method at constant pH. The affinity of material for CrO4 2anion was studied as a function of contact time, pH of solution and mass ratio of [Zn-Al-Cl]/CrO4. The removal of chromium effluent is a rapid process. Indeed, at pH 7 and at room temperature, the adsorption equilibrium is reached after 120 min and the kinetics follow a pseudo second order model. The adsorption isotherm is in good agreement with the Langmuir model. The results show that retention of Cr(VI) by LDH is by adsorption to the outer surface and by intercalation between the layers of LDH via the anionic exchange reactions. Removal of Cr(VI) was confirmed by the XRD results (increasing interlamellar distance) and those of IR spectroscopy (appearance of characteristic bands). The percent removal of chromium VI by LDH reached 99.7% for LDH/CrO4 mass ratio equal to 3 with a maximum amount retained of 247,86 mg/g as ions CrO4 2-