Treatment Of De-magging Liquor Of Phosphate Ore And Preparation Of Magnesium Ammonium Phosphate Hexahydrate

When low-grade phosphate ore is transformed to high-grade phosphate ore via mixed phosphorus and sulfur acid leaching, a lot of de-magging liquor containing magnesium (Mg), phosphorus (P) and other metal ion is produced. If the de-magging liquor is reused directly, it will affect the extraction of magnesium from phosphate ore. If the de-magging liquor is discharged directly, resources will be wasted and the environment will be polluted. In this thesis, precipitation condition for each metal ion was studied theoretically and experimentaly, and the impurities were removed. The effecting factors of the preparation of magnesium ammonium phosphate hexahydrate by adding ammonia or ammonium salt into the de-magging liquor were studied. The main research contents and conclusions are as follows:(1) The existing forms and distribution coefficients of each ion in solution were analyzed theoretically. The minimum concentrations for each ion to precipitate were calculated. The results showed that Fe3+、Al3+、Ca2+ will precipitate in order, as the pH increases. So Fe3+、Al3+、Ca2+ can be removed from the solution in a right pH range. If the concentration of the solution is higher, the pH value of solutionin which Fe3+、Al3+、Ca2+ can be removed will be lower, and the rang will be more narrower. The first, the second, the third de-magging liquor can be efficiently purified in the pH value range of 4.1～5.2,3.4～4.3,3.4～3.8, respectively.(2) Sodium hydroxide solution and sodium carbonate solids were used to regulate the pH value of the third de-magging liquor, respectively.The results showed that sodium carbonate solids is better than sodium hydroxide solution when they areused to purify the third de-magging liquor. And the best conditions are as follows:the pH value is 4, the reaction time is 20 min, the reaction temperature is 25℃, the stirring speed is 200 rpm.Under such conditions, the removal rates of Fe3+, Al3+ and Ca2+ are 99.00%,99.80% and 91.20%,respectively. And the loss rates of Mg2+ and H3PO4 are 4.80%,9.20% respectively. When sodium carbonate solids were used to purify the first and the second de-magging liquor, the optimum pH values were 4.5 and 4.0, respectively. The results of tests are well coincident with those of theoretic calculation.(3)Ammonia, aqueous ammonia, aqueous ammonia and sodium hydroxide were compared when they were used to recycle magnesium and phosphorus in the third de-magging liquor which had been purified for preparation of magnesium ammonium phosphate hexahydrate from theoretical and experimental analysis. And the possibility of by-products formation were analysised. According to the results, the precipitant composed of ammonia and sodium hydroxide has the obvious advantages, the adding quantity of ammonium were decreased significantly, the recovery rates of magnesium and phosphorus increased, the purity of product almost kept unchanged, and the residual concentration of NH4+ in filtrate decreased significantly. When N:Mg ratio was 1.1:1, pH value of solution was 6.0, the recovery rates of magnesium and phosphorus were 98.60%,52.51%, respectively, the purity of magnesium ammonium phosphate hexahydrate is 97.94%, the residual concentration of NH4+ in filtrate is 581.92 mg·L-1.