| 摘要 |
<p>Mixed polyphosphates of sodium and potassium of general formula (Na,K)x+2PxO3x+1 wherein x/sF 2 are prepared by treating calcium phosphate ore with a solution of H3PO4 and sodium or potassium sulphate, filtering off the solids containing CaSO4 and partially neutralizing the filtrate with a basic sodium and/or potassium compound, e.g. oxide hydroxide carbonate, or bicarbonate, then filtering and finally evaporating, and calcining to form the polyphosphate. The amount of sulphate added is such as to convert into CaSO4 all the calcium ions in the phosphate ore. The amount of base added is such that the ratio of sodium and potassium ions to phosphorus atoms is equal to x+ 2/x . If the H3PO4 solution is impure it can be treated with Na2SO4 and any impurity such as Na2SiF6 is removed as a separate step. Any SO4- ions present in the solution after the filtering off of the CaSO4 may be removed by adding a Ba salt as a separate step and filtering. The process may be continuous. The Na: K ratio in the product is preferably 0.3 to 0.7:1. The amount of H3PO4 added may be such that the solution has a P2O5 content of 25 to 35% weight. The K2SO4 and ore that are used in the first stage may be ground. The amount of K+ ions added in the first stage can be such that the K2O/P2O5 ratio is below 0.5 and this reaction time is 2 to 6 hours at a temperature between 35 DEG and 55 DEG C. During the neutralization the reaction time may be 1/2 to 2 hours at temperatures between 50 and 100 DEG C. The evaporation may be to a salt concentration of 48 to 55% weight when some of the calcined product can be added. Calcination may be at a temp. between 250 DEG and 500 DEG C.</p> |
