Study On The Process Of Preparing Ammonium Phosphate And By-Product Calcium Sulfate Whisker By Hydrochloric Acid-Double Salt Precipitation

In this dissertation,"hydrochloric acid-double salt precipitation method"was designed to prepare ammonium phosphate and by-produce calcium sulfate whiskers,using medium-grade phosphate ore as raw material on the basis of comprehensive literature review and preliminary research.The main purpose is to overcome the current shortage of high-grade phosphate ore resources in our country,as well as the difficulty in the separation of phosphoric acid and calcium chloride in the solution and the problem in the comprehensive disposal of the calcium chloride solution after separation in the hydrochloric acid method wet-process phosphoric acid process.The main technological conditions,such as,the precipitation of double salt,the disposal of calcium chloride solution and the preparation of ammonium phosphate were optimized.The main conclusions were as follows:?1?The suitable process conditions of the mela mine phosphate double salt precipitation process in the 100 mL reaction system were as follows:reaction temperature 30?,the concentration of phosphoric acid solution 0.6 mol·L^-1,the molar ratio of mela mine to phosphoric acid 2:1,reaction time 120 min,and the mass ratio of mela mine added in two steps 2:1.The repeated experiments under the optimum process condition indicated that the average precipitation rate of phosphoric acid was 86.86%.?2?When the concentration of phosphoric acid solution is 0.6 mol·L^-1 and the mass ratio of mela mine added in two steps is 2:1,the suitable process conditions of the precipitation of the mela mine phosphate double salt in the 500 mL reaction system were as follows:reaction temperature 30?,reaction time 2.5 h,the molar ratio of mela mine to phosphoric acid 3:1.The repeated experiments under the optimum process condition indicated that the average precipitation rate of phosphoric acid was 86.71%.?3?DTAB was selected as the more suitable crystal form control agent for the preparation of calcium sulfate dihydrate whiskers and the suitable process conditions were as follows:the addition of DTAB 3%?mass percentage?,reaction temperature90°C,the concentration of Ca²⁺0.1 mol·L^-1,reaction time 25 min,and the molar ratio of calcium to sulfur was 1.1:1.The repeated experiments under the optimum process condition indicated that the calcium sulfate dihydrate whiskers prepared were relatively uniform in morphology,and the aspect ratio reached to about 130:1.?4?The analysis about the action mechanism of the crystal control agent indicated that:DTAB ionizes in the water to produce the surface active ions with positive charge,which will selectively adsorb on the side of the crystal with negative charge Ca SO₄·2H₂O,reducing the side surface energy and slowing down the growth rate in this side,thus promoting the growth of the whisker along the axis of the top,and whiskers with a longer diameter are obtained.?5?The suitable process conditions of the ammonolysis process of mela mine phosphate were as follows:reaction temperature 65?,the mass fraction of ammonia water 9.5%,and reaction time 50 min.The repeated experiments under the optimum process condition indicated that the average ammonolysis rate of mela mine phosphate reached to 96.00%.According to the analysis of the XRD patterns,the main component of the recovered solid was mela mine,and the prepared white crystal sample was monoammonium phosphate containing a small amount of unknown impurities.