Evaluation of rice husk biochar modified with magnesium oxide in adsorbing heavy metals from tannery wastewater

Abstract

Tannery wastewater contains heavy chemicals that are dangerous to the environment, as well as to human health. Lead, cadmium, and chromium are known to cause nervous disorders, cancer of the lung, skin diseases, and sudden death. The removal of heavy metals from the ecosystem is a global concern, and many methods like electroplating, ultrafiltration, and reverse osmosis, have recorded success in removing heavy metals from wastewater. However, they are expensive and require sophisticated technology, thus necessitating the need to develop cheap and affordable adsorbents for adsorbing heavy metals from the wastewater. Biochar derived from the agrowaste materials and modified with nanoparticles, such as magnesium oxide (MgO) have high surface area, cation exchange capacity, and diverse functional groups, making it suitable for adsorbing heavy metals and other pollutants from wastewater. For this reason, rice husk and MgO were pyrolyzed at 500 ^o C, at a residence time of two hours to produce an adsorbent (RHBMgO@500) for adsorbing lead, cadmium, and chromium from the tannery wastewater. An Atomic Absorption Spectroscopy (AAS) was used to determine the removal efficiency of RHBMgO@500 for lead, cadmium, and chromium, and the results revealed the removal efficiency for lead as 43.09% to 93.518%; for cadmium as 19.17 % to 86.30%, and for chromium as 85.793 % to 100.00 %. Its adsorption capacity for lead, cadmium, and chromium were 0.43mg/g to 0.858mg/g, 0.00028mg/g to 0.0027mg/g, and 58.073mg/g to 232.200mg/g respectively. For the optimization, the Ramp graph function from the response surface methodology (RSM) based on the central composite design (CCD) showed that temperature, contact time, pH, and adsorbent dosage are set to 41 ^oC, 45 minutes, 6, and 4g, respectively, the removal efficiency for lead, cadmium, and chromium can be 62%, 62%, and 100%, respectively.