磷石膏在低浓度硫酸中的溶解及相态变化

Research of the dissolution and phase behavior change on the phosphogypsum in the low concentration of sulfuric acid

湿法磷酸生产过程副产大量磷石膏，因其含有较多杂质而无法直接利用，目前可采用硫酸酸浸处理提高磷石膏品质。为弄清酸浸过程中石膏的溶解性能和结晶形态的变化，本文探讨了在0～80℃、0～30%的硫酸浓度条件下，磷石膏在硫酸溶液中的溶解度大小、结晶形貌、物相组成及结晶水含量的变化情况。实验结果表明，磷石膏在硫酸溶液中的溶解度随温度升高而升高，在80℃时达最大；随浓度升高呈先升后降的变化，在硫酸浓度为10%时溶解度最大。硫酸浓度小于10%时，磷石膏中二水硫酸钙溶解，但无新相生成，其形貌变化不大；硫酸浓度大于10%时，二水硫酸钙溶解，同时再结晶转化成无水硫酸钙，最终导致磷石膏形貌和相态发生了改变，溶解度随硫酸浓度升高而降低。

Phosphogypsum is a by-product in the production process of wet-process phosphoric acid. The impurities in phosphogypsum limit the usage of it. Sulfuric acid leaching processing can be used to improve the quality of phosphogypsum. In order to clarify the changes of dissolution performances and crystalline morphologies of phosphogypsum in the acid leaching process,this paper investigated the solubility size,crystal morphology,phase composition and the changes of crystal water contents of the phosphogypsum in the sulfuric acid solution at 0-80 ℃ and 0-30%of sulfuric acid concentration. The results showed that the solubility of phosphogypsum in sulfuric acid solution increased with the increasing temperature and the maximum solubility was at 80 ℃. As for the changes of concentration,the solubility increased at first and then decreased and the highest solubility occurred at the sulfuric acid concentration of 10%. When the sulfuric acid concentration was lower than 10%,the dihydrate calcium sulfate in the phosphogypsum dissolved with no new phase formation,and the morphology of phosphogypsum did not change much. When the sulfuric acid concentration was greater than 10%,the dihydrate calcium sulfate dissolved and recrystallized into the anhydrous calcium sulfate,eventually leading to the changes of phosphogypsum morphology,phase state and the increase in solubilty.