At present,a large part of China's phosphoric gypsum is used as a substitute for natural gypsum and further processed into various kinds of construction products.Recently the revision of Building Gypsum,a national standard,has come down soliciting overall public opinions.In the former national standard phosphoric gypsum was defined as waste slag containing dihydrate calcium sulfate as its main constituent remaining after ammonium phosphate is made,in this revision it will be redefined as a by-product containing dihydrate calcium sulfate that is taken after extracting phosphoric acid from phos-phorus ore.
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