The Study On The Technology Of Preventing Blockage In Recirculating Water Systems Of Phosphogypsum Stacking

At present, water shortage and water pollution have attracted great concern. The recycling of the industrial waste to solve the water shortage problem has attracted great interest. The waste water from the production of phosphoric acid and from the seepage of phosphogypsum consolidation was collected and recycled. Duringthe recycling of waste water, thecrystallization of inorganic salts in the waste water would clog the pipeline and pump and affect the circulating of water. The main crystalline salts are K2 Si F6, Na2 Si F6 and other insoluble salts, which are difficult to be cleaned from the pipeline and pump. Therefore, it is very important to study the crystalline mechanism of the circulating system in order to solve the clog problem.The main findings in the work are as follows:(1)The solubilities of K2 Si F6 in sulfuric acid solution with different p H values at273.15~313.15 K were determined by the equilibrium method. The solubility data correlated by Apelblat empirical equation are very important phase equilibrium data for design. Under stirring, the growth of K2 Si F6 crystal is controlled by surface reaction. According to Arrhenius equation,the activation energy of crystallization is 53.21 k J/mol. The kinetic equation is(2)The influence of temperature on crystallization of K2 Si F6 and crystal precipitation was studied with the recycled water of chemical company. The results show that the main crystalline saltsare K2 Si F6 and Na2 Si F6, as well as small amounts of Ca SO4?2H2O. The crystallization temperature of K2 Si F6 in the recycled water is 14℃. Under stirring, the growth of K2 Si F6 crystal in the recycled water is controlled by the surface reaction. The activation energy of crystallization is 40.36 k J/mol. The kinetic equation isWithout stirring, the growth of K2 Si F6 crystalin the recycled water is controlled by surface diffusion. The activation energy of crystallization is 40.36 k J/mol. The kinetic equation isThe formation of K2 Si F6 crystalcan be inhibited by adding lime and aluminum compounds, due to the redecreased concentration of Si F62-, leading to decreased concentration of K2 Si F6 and decreased temperature for crystallization. The results indicate that when the additions of Ca O, Al Cl3 and Al2(SO4)3 are 2.21 g/L, 1.10 g/L and 1.35 g/L, the crystallization temperatures of K2 Si F6 decrease by about6℃, 6℃and 7℃, respectively. The optimum additions of Ca O, Al Cl3 and Al2(SO4)3 are 2.21~5.35 g/L, 1.10~3.82 g/L, and 1.35~5.17 g/L, respectively.(3)Three experimental schemes were designedby considering the structure of circulating-water system: ventilation cooling, adding chemical additives, reducing the degree of supersaturation by dilution and improving the technology for phosphoric acid production. Ventilation cooling and waterdilutionarenot feasible based on the calculated cost of experimental scheme. The cost of adding Al2(SO4)3 is relatively small and the operation is relatively easy.