Physicochemical and Technological Principles of Potassium Hydroxide Production by Causticization of Potassium Carbonate with Lime Milk

Abstract

The physicochemical and technological principles underlying the production of potassium hydroxide through the causticisation of potassium carbonate with lime milk were studied. The influence of the K2CO3 solution concentration, the concentration of lime milk, and the Ca(OH)2 dosage on the composition of the liquid and solid phases, the KOH yield, and the settling, filtration and washing characteristics of the precipitate was examined. Conversion was carried out at temperatures up to 95 °C for 90 min. The results showed that the yield of potassium into the target product under the studied conditions was 76.74–85.19%. X-ray phase analysis of the washed precipitates showed a predominance of CaCO3 (91.04–94.50%) with a residual Ca(OH)2 content of 5.50–8.96%. The rheological characteristics of the suspensions were examined in the range of 20–80 °C at a KOH content in the liquid phase of 5–30% and an S:L ratio of 1:2 to 1:4. The density of the suspensions varied from 1.136 to 1.534 g/cm3, and the viscosity from 2.42 to 9.68 cP. Three-stage washing was found to be suitable for the near-complete washing of the precipitate; after the third stage, KOH was no longer detected in the precipitate, and the K2CO3 content decreased to 0.07–0.26%. Subsequent evaporation of the filtrate can increase the KOH concentration to 73.81%. The results obtained provide a basis for the design of a resource-saving process flow sheet for the production of liquid and concentrated potassium hydroxide with the return of wash water to the process.