Optimization of microwave assisted synthesis of activated carbon from biomass waste for sustainable industrial crude wet-phosphoric acid purification

Crude phosphoric acid, generated during industrial wet production, requires careful treatment by different processes to make it acceptable for various agro-industrial applications. The purification of crude phosphoric acid is still challenging and costly at a large scale because of the presence of various organic and inorganic pollutants. The adsorption technique for the purification of crude phosphoric acid suffers from the low sorption rate due to its complexity in terms of chemical composition and low pH. To enhance the sorption selectivity, the texture and surface chemistry of activated carbon should be well designed via the optimization of synthesis conditions. The present work aims to valorize local biomass waste (palm petiole, PP) into highly mesoporous adsorptive activated carbon (ACPP) for the removal of the organic matter (OM) from crude industrial phosphoric acid (26% P2O5). The microwave-assisted synthesis of ACPP was optimized using full factorial design (FFD) and analysis of variance (ANOVA). Experimental factors that govern the removal of OM from phosphoric acid using ACPP were investigated to maximize the purification rate. Even though the yield of OM in phosphoric acid is high, ACPP removes about 81.5% of OM. Several parameters were studied to optimize and understand the adsorption behavior of OM on the surface of ACPP. The adsorption process undergoes pseudo-second-order kinetic, and the adsorption isotherm follows the Sips model. Overall, this research shows that the carbonization of biomass assisted by microwave and the use of H3PO4 as activation agent produces a highly adsorptive activated carbon with high affinity towards removing OM from crude phosphoric acid. Optimizing biomass waste carbonization factors by facile and sustainable routes would benefit industries to produce pure phosphoric acid at a low cost and eco-friendly route.