Potassium-phosphorus-sulfur augmented biochar production from potentially toxic elements abated gypsum pond wastewater of phosphate fertilizer industry

Abstract

Present study highlights scope and process for production of environmentally safe (reduced F, Cr, Cd content) and multi-nutrient (K, P, S) enriched biochar utilizing highly acidic gypsum pond wastewater (GPW; P and S rich) and banana peduncle (K rich) waste. Untreated and treated [potentially toxic elements (PTE) adsorbed on Crassostrea shells] GPW soaked biomass pyrolyzed at 400, 600, 800 °C and produced K-P-S enriched biochar (KPS-B-400/600/800 and T-KPS-B-400/600/800). Physicochemical characteristics of biochar were investigated by XRD, FTIR and surface area analyser. The K, P and S contents were 14–15.53, 1.88–2.27 and 3.75–4.77% in the untreated biochar produced at 400, 600 and 800 °C respectively, with corresponding values of 15.21–18.43, 2.05–2.91 and 0.62–1.09% in the treated biochar. At various temperatures, K, P and S formed mineral phases such as K(H2PO4), KH5(PO4)2, K2CaP2O7 and K2SO4 in untreated biochar, and K3P, K2SiP2 and K2S in treated biochar. Sulfite (SO32-) was identified as pre-dominant functional group in untreated and treated biochar. Water soluble and Toxicity Characteristic Leaching Procedure (TCLP) F contents in T-KPS-B-800 were lowered to 0.005% and 0.013% respectively and values were well below permissible limits. Toxic Cd TCLP content reduced by 5.75% in T-KPS-800 over KPS-800, whereas Cr reduction of 44% was eastimated in T-KPS-400 with respect to KPS-400 due to treatment of GPW with molluscan shells. Above findings establish an alternative way of nutrients recovery and PTE reduction from phosphate fertilizer industry GPW.