부산대학교 도서관

A method according to this invention is used for washing waste phosphogypsum produced at decomposition of a mineral phosphoric raw material with sulphuric acid, wherein the said washing is carried on in countercurrent on a multi-zone filter; to the last zone of this filter there is supplied water while filter washings with highest concentration of the component being washed-off are returned to the decomposition stage. The essence of this method consists in that to the washing liquids there is introduced sulphuric acid solution of a concentration of sulphuric acid ranging within the limits from 20 up to 98 percent by weight of sulphuric acid in the amount of 1 to 30 percent of sulphuric acid amount used for decomposition of a phosphoric raw material. Sulphuric acid solution may be introduced either directly to the washing zones, or to the filter washings, or it may be used, first, for washing the filter cloths and next directed to the washing zones, or first introduced to a condensate produced at the time of cooling down the reaction pulp and then used for washing the filter cloth and, finally, introduced to the remaining washing zones.