The Study On Feed Dicalcium Phosphate--Digestion And Sludge Separation

The diluted hydrochloric acid of 11-18%, as byproduct of the thermo-chlorination chloromethane plant of HCIC (Honghe Chemical Inc.), is used to produce the feed dicalcium phosphate in the process of two section neutralization with non-sludge separation and mixing defluorination methods. Because a lot of impurities such as ions of Fe, Al, F, Mg and Si exist in the acid digestion solution as well as engendered colloid, it will overly decrease production capacity, and thus cause a series of problems like phosphor loss and environment pollution.This paper discusses problems of the acid digestion and sludgy separation of normally production route for feed dicalcium phosphate and further put forward a new method. The study involves several hands, which include that: A) Study on digestion kinemics and effects of impurities so as to obtain a optimizing control condition; B) Study on flocculating and precipitation of colloid and acid-indiscerptible materials in order to find suitable operation condition; C) Contrasting between centrifugal separation and vacuum filtering experiments in a flat bottom funnel filter, and recommend a optimizing filtering controlling condition. Based on these results, a new production route of dicalcium phosphate is discovered, which possess of two-section neutralization after sludge separation. The process can be simply described below. The sludgy after digestion is firstly settled without neutralizing. Pellucid liquid through precipitating and filtering is used to make firstneutralization so that it can get rid of heavy metals, fluorine and a little part of dicalcium phosphate that can be used as fertilize. The surplus solution is neutralized again, and the final deposit by drying is just product of feed dicalcium phosphate. Because of this, the production yield increase to 72% from 58-61%, and the waste residue is reduced to 265 kg/ ton-product from 1-1.5 ton/ton-product. The economic and environment benefits are much more favorable.The research results will not only open the bottleneck restricting production in normal process without precipitating sludgy, but develop a new production route which can enhance the production ability while making a small part change to the system and invest a little of funds.The new process is proved to be reasonable, reliable and creative. The technology features are as following: 1) Design the digestion unit according to the reaction between HF, H2SiF6 and Ca ion as well as kinemics condition. 2) Add flocculants according to the filtrating rate and the colloid-settling rate. 3) Jet the high concentrated lime-milk to the tank for improving crystallinity. 4) Possess great operating flexibility to fit change of raw materials.