Josephine Urayayi1, Hardlife Rambwawasvika2 and Washington Mutatu2
1Midlands State University Private Bag 9055, Gweru, Zimbabwe
2Zimbabwe Sugar Association Experiment Station, Private Bag 7006, Chiredzi, Zimbabwe; wmutatu@zsaes.org.zw
Stillage contains considerable amounts of potassium, which has attracted its use for fertigation. The infrastructure that is needed for fertigation requires huge capital investment, so that only fields close to the ethanol plant benefit, albeit salinising the soil, and acidifying and destroying the conveyance infrastructure. Making baggable potassium sulphate is a way of mitigating the challenges of stillage fertigation. This idea has been validated at a laboratory scale through the wet digestion method. In this scaled-up model, stillage from the Triangle Ethanol Plant was analysed for its elemental constituents. It contained 2.20% (± 0.18%) of potassium. The extracted potassium was recovered as potassium sulphate through the processes of digestion, clarification, evaporation, crystallisation and decolourisation. The optimised process produced 1.13 kg of potassium sulphate with a purity of 95.79% from a 60 L batch of stillage. The cost of producing potassium sulphate from stillage was cheaper by 26.96% than for the commercial product.