Sustainable methodology for production of potassic fertilizer from agro-residues: Case study using empty cotton boll

Potassic fertilizer was synthesized from cotton boll ash retrieved after solar gasification at 1100 °C. The ash was leached through batch-wise multistage countercurrent leaching, while the parameters were optimized using Response Surface Methodology. A face-centered central composite design was employed to scrutinize the effects of four independent variables- number of leaching stages, solvent to ash ratio, leaching time and particle size while the investigated response variable was K + leaching efficiency, defined as the ratio of extracted K + to total available water-leachable K + in the ash. The validated model achieved a desirability of 0.92 and identified the optimal operating leaching conditions with a predicted K + leaching efficiency of 98.8%. For synthesis of potassic fertilizer, routes of fractional crystallization and selective precipitation (using tartaric acid) were studied; the former recovers 97% of potassium as K 2 SO 4 and KCl whereas the latter recovers 94% as KNO 3 .