Method of lowering the magnesium impurity level of wet-process phosphoric acid during production of liquid fertilizer

摘要

A process for treating wet-process weak phosphoric acid solution is disclosed which significantly lowers the magnesium impurities in the acid (as well as certain other impurities) permitting subsequent concentration of the acid to levels for use in preparation of liquid fertilizers which are less prone to settling out of the impurities during storage than would be the case without such treatment. It has unexpectedly been found that by limiting evaporation of water from the initial 26% to 32% P.sub.2 O.sub.5 wet-process acid to a level such that the acid has a P.sub.2 O. sub.5 content of from about 42% to about 45% and thereafter maintaining the semi-concentrated acid at a temperature within the range of from about 145° F. to about 270° F. for an aging period containing of from about 24 hours to about 144 hours magnesium impurity crystals are formed of a size, shape and density such that when the acid is subjected to conventional centrifugation, a significant proportion of the magnesium impurities are removed from the acid to substantially avoid heretofore encountered problems associated with precipitation of magnesium compounds during storage of liquid fertilizers prepared from the magnesium purged concentrated acid.