Recycling of nepheline sludge into effective sorbents for deep purification of chromium-containing wastewater

The purpose of this work is to evaluate the potential of nepheline sludge formed at the Achinsk Alumina Combine as an effective sorbent for industrial wastewater treatment from hexavalent chromium (Cr(VI)). Laboratory experiments have been conducted to study the adsorption capacity of sludge. The chemical composition and structure of the samples were determined by X-ray fluorescence and X-ray phase analysis. The microstructure is assessed using scanning electron microscopy. X-ray phase analysis revealed that the main components of the sludge are calcium carbonate and dicalcium silicate. High levels of dispersion and alkalinity of the material are noted. Electron microscopy has shown a porous sludge structure providing a large available surface for sorption. It has been established that heat-treated nepheline sludge exhibits high sorption activity with respect to Cr(VI) ions. Increasing the processing temperature increases the specific surface area of the material and the number of active centers, contributing to the effective capture and neutralization of chromium ions. Changing the pH of the medium also has a positive effect on the sorption process. The test results showed that the use of sludge makes it possible to reduce the concentration of Cr(VI) to levels that meet the regulatory requirements for wastewater discharge into water bodies. The use of this waste will reduce dependence on imported reagents, reduce the volume of stored waste and improve the environmental situation in the region. The porous structure of the sludge ensures effective interaction with pollutants. Thus, the conducted studies confirm the prospects of using nepheline sludge as an effective and economically feasible sorbent for industrial wastewater treatment from hexavalent chromium.