Thermodynamics?Dynamics Investigation Of Ammonium Dihydrogen Phosphate And Optimization

Ammonium dihydrogen phosphate?ADP?is an efficient compound fertilizer and industrial raw materials.ADP fertilizer on the market usually contains a large quantity of impurities,and there are some problems in the production of ADP such as irregular shape,small and uneven crystal size,etc.which reduces the fertilization effect greatly.In this thesis,the investigation on the crystallization of ADP was performed.The main work and results are as follows:The solubility of ADP in water was measured by static analysis method,and the effect of Na⁺,SO₄^2- and tributyl phosphate?TBP?on the solubility was investigated.The results were correlated by Apelblat equation,which showed a good fit to the experimental data.The metastable zone widths?MSZW?of ADP aqueous solution at different temperatures were measured by laser method,under different agitation rates,different cooling rates and different TBP concentrations,and the apparent nucleation order was calculated.The results showed that none of the above impurities had significant effects on the solubility;TBP widens the MSZW,but Na⁺ and SO₄^2- narrow the MSZW;Also,the MSZW narrows down with increasing temperatures and agitation rates,while widens with increasing cooling rates.The induction time of ADP was measured by laser detection technique,and the nucleation parameters and the nucleation mechanism were studied;The kinetics data was measured by batch dynamic methods,and the nucleation rate equation and the growth rate equation were calculated.The results showed that the induction time decreases with the increasing degree of supersaturation,while TBP enlarges the induction time;When TBP exists,the surface tension,the critical nucleation free energy and the critical nucleation radius increase.The effect of agitation rate,cooling rate,keeping crystal and Ostwad's process on the cooling crystallization process of ADP was also investigated.The results showed that when the agitation rate is 180-220 rpm and the cooling rate varies slowly first and then fast,the impurity concentration reduces and crystal size distribution is uniform and modest;After keeping crystal and aging,the crystal size distribution narrows down and gets uniform;Also,after keeping crystal,the concentration of Na+gets less,but aging has no obvious effect on impurity concentrations.