Utilizing of sunflower ash in the wet conversion of phosphogypsum – a comparative study

•Valorization of sunflower ash as a cheap source of potash.•Water leaching of sunflower ash at 20 °C yields 0.2 t K2CO3 per 1 t of biomass.•A sustainable conversion method of phosphogypsum with sunflower ash was justified.•Phosphogypsum treating by K2CO3 from sunflower ash provides a profit of 2300 USD/t. Nowadays, there is a tendency to consider large-scale technogenic waste not as waste, but as man-made mineral deposits. For example, phosphogypsum is today considered a source of building materials, fertilizers, rare earth elements, etc. A similar problem is typical in the agricultural sector, whose waste is recycled inefficiently, especially in developing countries. Research in both directions is now on the rise, and the most relevant are those that involve the simultaneous disposal of two or more types of waste. This article critically compares the methods of wet conversion of phosphogypsum by ammonium, sodium, and potassium carbonates. Since the sunflower ash is a cheap source of potash (K2CO3 constituting up to 40% of biomass weight), simultaneous utilization of both agricultural and industrial waste could be achieved. It was found that the leaching of sunflower ash with tap water with preliminary aeration at temperatures below 30 °C provides a K2CO3 yield of about 200 kg/t. The resulting aqueous solution of potash can be processed into commercial salt or used directly for the conversion of phosphogypsum. As a result of such processing, a solution of potassium sulfate – a costly mineral fertilizer, as well as construction chalk, can be obtained. The most valuable elements of phosphogypsum are concentrated in that chalk – strontium and rare earth elements; their isolation into individual compounds can be carried out using appropriate techniques. The method of phosphogypsum conversion by potash solution obtained from water leaching of sunflower ash provides the maximum economic effect – 2300 USD per 1 t of phosphogypsum. [Display omitted]