Research On The Efficient Preparation Of Microfine Calcium Carbonate From Phosphogypsum

As an inorganic filler,calcium carbonate is widely used in various fields such as rubber,plastics,and building materials.Its common source is limestone,but it is not easily and economically mined,so the use of other low-cost calcium-containing raw materials to prepare calcium carbonate is of increasing interest.At the same time,the accumulation of phosphogypsum not only takes up a lot of valuable land resources,but also has a bad impact on the surrounding environment.The use of phosphogypsum instead of limestone as raw material for calcium carbonate preparation can not only protect the mining resources,but also prepare calcium carbonate with good performance and application prospects.In this paper,the Ca²⁺leaching process of phosphogypsum in sodium hydroxide,ammonium acetate and sodium D-glucose solution was studied respectively,and the effects of solution concentration,solid-liquid ratio,reaction temperature and reaction time on Ca²⁺leaching were analyzed,combined with x-ray diffractometer,video microscope and other microscopic means,the effects of ammonia addition,CO₂concentration,carbonization time of calcium carbonate prepared by carbonization and the process conditions such as material addition,temperature and reaction time of calcium carbonate prepared by complex decomposition on Ca²⁺conversion,crystalline morphology and particle size of calcium carbonate were revealed.and the best process method for the efficient preparation of fine calcium carbonate from phosphogypsum was obtained by comprehensive evaluation of calcium carbonate production rate,particle size,cost and energy consumption through SPSS software,and the applicability of this method and the possibility of filtrate recycling were discussed.The main conclusions are as follows:（1）The order of the magnitude of Ca²⁺leaching rate of phosphogypsum under different solutions was sodium gluconate（100.37%）>ammonium acetate（97.9%）>sodium hydroxide（93.13%）,The Ca²⁺leaching rate of phosphogypsum increased with decreasing solid-liquid ratio and increasing solution concentration under all three solutions.Under Na OH-HCl solution,Ca²⁺leaching rate did not change significantly from 25°C to 55°C;Under ammonium acetate solution,Ca²⁺leaching rate of phosphogypsum was elevated by increasing temperature,and above 65°C,impurities or ammonium gypsum inhibited Ca²⁺dissolution and Ca²⁺leaching rate decreased;under sodium gluconate solution,impurities promoted Ca²⁺leaching at 25°C-65°C and Ca²⁺leaching rate decreased at 85°C.（2）The phosphogypsum leachate was prepared by carbonation to prepare calcium carbonate.Under different solutions,the increase of ammonia addition,the increase of CO₂concentration and the increase of carbonation time would promote the continuous conversion of Ca²⁺.When the ammonia addition increased and CO₂concentration increased,the small size of calcium carbonate increased.When the carbonation time was prolonged,the size of calcium carbonate became larger under Na OH-HCl solution and ammonium acetate solution,which were large spheres;under sodium gluconate solution,the size of calcium carbonate became smaller,which were small spheres.（3）The phosphogypsum leach solution was prepared by complex decomposition to prepare calcium carbonate.Under different solutions,the increase of ammonia addition,the increase of NH₃HCO₃/Na₂CO₃addition and the increase of reaction time would promote the conversion of Ca²⁺.Under Na OH-HCl solution,the temperature increased,impurities inhibited Ca²⁺conversion and Ca²⁺conversion decreased;impurities retard the crystallization of calcium carbonate under ammonium acetate solution and sodium gluconate solution.At times longer than 60 min as well as the former at a temperature of 65°C,partial dissolution of calcium carbonate occurs and Ca²⁺conversion decreases.The nucleation and growth of calcium carbonate were jointly controlled by ammonia addition,NH₃HCO₃/Na₂CO₃addition,and temperature.The composition of the solution affected the crystallization mode of calcium carbonate,and the morphology and particle size of calcium carbonate varied greatly with different conditions.（4）The calcium carbonate crystals obtained by carbonization preparation under Na OH-HCl solution and ammonium acetate solution were all a mixture of vaterite and calcite,and under other process methods,the calcium carbonate crystals were pure calcite.（5）The weights of calcium carbonate generation rate and particle size were 26.8%and28.1%,respectively,and the overall evaluation ranking was,P _complex（0.245）>Q _carbon（0.218）>C _carbon（0.200）>P _carbon（0.115）>C _complex（-0.311）>Q _complex（-0.467）.The optimal process conditions were:phosphogypsum in 1 mol/L sodium gluconate solution at a solid-liquid ratio of 1:30 and a temperature of 25°C,after 10 min of reaction,the insoluble impurities were filtered,and subsequently the leachate was added with 6g Na₂CO₃at a temperature of 25°C and reacted for 1 h.（6）Under the efficient preparation of fine calcium carbonate method,calcium carbonate was prepared using phosphogypsum of different purity,and the calcium carbonate production efficiency was above 99%,and the purity was between 85-90%.When the purity of phosphogypsum is low,the soluble impurities contribute to the small size of calcium carbonate,and the morphology is not significantly different.（7）The first three cycles of carbonation filtrate under the best process conditions,the reaction efficiency were above 99%,the purity,particle size and morphology of calcium carbonate did not change significantly,and crystallization separation could be used to achieve the recycling of sodium gluconate.