| Phosphogypsum（PG）is an industrial solid waste from the wet production of phosphoric acid.In recent years,with the rapid development of phosphating industry,phosphogypsum which is difficult to use is piled up in large quantities,occupying a large amount of land,and seriously polluting the ecological environment.Therefore,it is urgent to solve the problem of efficient resource utilization of phosphogypsum.This paper presents the research idea of using phosphogypsum to prepare Belite sulfoaluminate cement（BSAC）.Gaseous sulfur is used to reduce phosphogypsum to form Ca S,and intermediate product Ca S reacts with unreduced phosphogypsum to form Ca O as the total calcium source,thus greatly increasing the intake of phosphogypsum,which has certain theoretical and practical significance for the resource utilization of phosphogypsum.The above research ideas can be simplified into three stages: reduction of phosphogypsum,decomposition of phosphogypsum and clinker firing.In the reduction stage of phosphogypsum,the main control parameters are as follows: the content ratio n（Sgas）/n（CaSO4）of sulfur and phosphogypsum is suitable between 0.4 and 0.52,and the appropriate reaction temperature window is small,between 850 （?）and 860 （?）.Nitrogen protection is required in the decomposition stage of phosphogypsum,and the calcining temperature is set at 1200 （?）for 30 min.Several calcination systems were designed to prepare Belet sulfoaluminate cement clinker.The mineral phase composition and content of cement clinker were determined by XRD,FT-IR,TG and NMR.Research results show that the raw material is easy to burn,clinker main mineral phases are C4A3（?）,C2 S,C4AF,containing a small amount of C2 AS and alpha’-C2 S.With the increase of calcination temperature and calcination time,C4A3（?） content increased,but more than 1300 （?）calcination temperature,calcination time after more than 90 min of C4A3（?）.The suitable sintering temperature range of cement clinker is 1280 （?）1300 （?）,and the suitable calcination time range is 60 min 120 min.The cement properties and hydration products of Belite sulfoaluminate clinker prepared by the above technical route show that: the hydration products of Belite sulfoaluminate cement prepared are mainly ettringite,C-S-H,C2ASH8 and AH3.The p H value of the sample cement alkalinity coefficient was lower than 10.3,and the cement slurry showed low alkalinity.The 3 d,7 d and 28 d compressive strengths of Belite sulfoaluminate cement fired by the best calcination regimes were 33.6 MPa,36.7 MPa and 43.1 MPa.The setting time of cement is short,the initial setting time is less than 15 min,and the final setting time is less than 20 min,showing fast setting characteristics.The shrinkage rate of cement mortar is 18.89% lower than that of 42.5 fast hard sulfoaluminate cement,showing low dry shrinkage.The properties of cement were optimized by changing the content of iron phase,mixing the proportion of limestone and gypsum and adding active oxides.The optimum iron phase content is 20.15%,The optimum ratio of clinker: limestone: gypsum ratio is 88:8:4,The optimal Ca O content is0.5%,The optimal Mg O content was 3.0%.This indicates that it is feasible to use gaseous sulfur reduction phosphogypsum as total calcium source to prepare Belite sulfoaluminate cement.Compared with traditional cement calcium source,this reaction process will greatly reduce carbon emissions and produce a large amount of SO2.When the decomposition rate of phosphogypsum is 91.97%,the theoretical concentration of SO2 in the tail gas can reach 18.32%,which has the value of collecting and producing sulfuric acid.Sulfuric acid can be prepared by co-production. |
