Composition, Properties and Using Fields of Product of Phosphogypsum Recycling

Abstract

Nowadays about 200 million tons of phosphogypsum (PG) have been stored in the dumps of the chemical industry and non–ferrous metallurgy of Russia which pollutes the environment. This waste contains up to 98 % of two–water gypsum and impurities including rare earth metals (REM) in an amount of up to 0.5 % preventing its use in the production of building materials. A complex technology of FG recycling including extraction of REM, neutralization and dehydration of the pulp for using in the production of gypsum binders and Portland cement. Results of determination of density, grain, chemical and mineral compositions and structure of the product of recycling of FG of the “Sredneuralsky copper smelting plant” are presented. After the REM extraction, the PG is a loose lumpy mass with moisture content of 28–32 % which contains about 10 % of particles larger than 40 mm and not more than 60 % of particles less than 10 mm, it has a true density of 2.26 g/cm3, pH of aqueous extract is 5.95. It has the following chemical composition, mass. %: 0.87 SiО2; 0.93 A12O3; 0.20 Fe2O3; 31.00 CaO; 0.034 MgO; 44.27 SО3; 0.10 K2О; 0.42 Nа2О; 0.45 Р2О5(general); 20.73 of mass loss of ignition. The mineral composition of the PG processing product is represented by two-water gypsum and a slight amount of quartz. The possibility of using gypsum–containing waste in the production of gypsum binders and cement is considered. The effect of temperature and duration of firing, the dispersion, the type and quantity of chemical and mineral admixtures on physical and mechanical properties of gypsum binder, the influence of the type and amount of mineral additive on pelletizing and physic–mechanical properties of the granulated and pressed PG and its effects on setting time and strength of Portland cement are represented. It is recommended to use PG to obtain low–temperature and composite gypsum binders, regulation of Portland cement setting after extraction of REM.