Potassium Fluoride From Recovered Fluoride In Wet Process Phosphoric Acid And By-product Silica Used In Slow-release Fertilizer

In today's era of resource-saving,making full use of wet process phosphoric acid industry resources has important economic and social significance.Slow-release fertilizer has the characteristics of a slow-release and long-term property,Outputting and using slow release compound fertilizer which was cheap,efficient,environmental and easily degradable was currently one of the trend of the development of the chemical fertilizer industry,and was the requirement for the strategy of the sustainable development and the development of ecological agriculture in the new century.The main purpose of this paper is the preparation of potassium fluoride with defluorization from wet process phosphoric acid and the preparation of slow release compound fertilizer which coated diammonium phosphate particles using its by-product silica.This research includes three parts: Firstly,the influence of different factors on the quality of potassium fluoride was studied and its purification mechanism was analyzed.Secondly,the influence of the different factors on the property of film-forming,water absorption and water retention of the silica film were investigated,the best preparation process route was achieved.Last,slow-release fertilizer was formed and sprayed from DAP with double wrapper,the inner envelope from modified silica which blended emulsion,and the outer envelope from wax.Adopting method of static water extraction,abrasion test of fertilizer particle and compressive strength test of the particles,the property of slow release,wear resistance and compressive strength of the fertilizer at different covering rate and different cladding coated situation were discussed,and the best covering rate was established.At the same time,the nutrient release characteristics of coated fertilizer was explored by the method of soil column leaching to establish its nutrient release kinetics.The main conclusions are as follows:?1?In purification process of the preparation of potassium fluoride,the terminal point of pH adjustment of preparative potassium fluoride solution is equal to the pH value of pure potassium fluoride solution whose mass percent concentration is the same,and controlling the percent mass concentration of potassium fluoride solution more than15% by adjusting water consumption then filtrating secondary at room temperature,the effect of purification is best.In the result,purity of KF increased upon 99%,and the yield was about 92%,the product of the indicators meet industrial requirements.At the same time,the by-product of silica including potassium nutrient is an excellent inorganic coating materials of fertilizer.?2?A water-absorbing and water-retentive inorganic-organic composite coating material was studied through an aqueous solution as a main solvent and silica modified by the addition of additives by high shear emulsification technique.The optimum ratio of raw materials and process conditions were as that: silica powder weighting 50 70,an aqueous solution of PVA weighting 400,HPMC or CMC weighting 3.5 4.5,glycerin weighting 7-9,silicone defoamers weighting 0.04 to 0.06.wherein the concentration of the aqueous solution of PVA is 4% ⁵%,blending stirring speed is 900 rpm 1100 rpm,the blend was stirred for about 40 min,the drying temperature is 80 ?⁹0 ?,coating materials prepared have a good property of film-forming,water-absorbing and water-retentive at present.?3?While the coated slow-release fertilizer was prepared with the DAP particles atomizedly sprayed by modified silica emulsion,we can find that the coated fertilizer were wrapped tightly and enveloped well by scanning electron microscopy analysis.according to the consequence of testing of abrasion resistance,compressive strength and sustained-release showed that: the covering rate of modified silica emulsion increased more,the abrasion resistance,compressive strength and sustained-release of fertilizer were better.When the covering rate reaching 40%,the initial nutrient accumulative release rate of fertilizer was less than 15% and 28-day nutrient cumulative release rate was less than 80%,so the product performance achieved the requirement of national standard of sustained-release fertilizer GB / T 23348-2009.?4?When the relationship between each nutrient release rate of coated fertilizers and leaching time was evaluated by the method of leaching in soil column,nutrient release rate of N and P were experiencing slow-fast-slow a process with the leaching time increasing,but N nutrient release faster than P.The nutrient release kinetics of themodified silica coated DAP fertilizer were studied and found in conformity with a model kinetic equation named Sugihara Q_t = Q₀ [1-exp?-kt?],and the relativity is well.