a simplified and enhanced process to produce thermofertiliser obtained from potassium and phosphorous - bearing minerals is provided , where these elements may or may not be in citric acid or insoluble in water . the process also includes the use of specific additives , at the beginning of the process or immediately before the beginning of the thermal treatment step , in order to increase the potassium and phosphorous contents in the product and the overall efficiency of the process and also to promote the production of a high quality thermofertiliser .