Abstract:

High-Mg phosphate tailing is a solid waste produced in the reverse flotation process of phosphate rock.The main mineral phase is dolomite，containing a small amount of fluorapatite and quartz.The phosphate tailing was dried and ground to produce phosphate tailing powder.The particle size distribution and toxicity of phosphate tailing powder were analyzed，and the related performance indexes were determined according to GB/T 51003—2014“Technical Specification for Application of Mineral Admixtures.”Concretes with different strength grades of C30，C40，C50 and C60 were prepared using cement，phosphate tailing powder and fly ash as gel materials.Working and mechanical properties of concrete were measured，and mineral composition of cement slurry with phosphate tailing powder at different hydration ages was analyzed.The results showed that the average particle size D₉₀ of the phosphate tailing was decreased from 133.1 μm to 63.4 μm after drying.The firing loss of phosphate tailing powder was 39%，the 28 d activity index was 70%，and the methylene blue value was less than 1.4.The fluidity ratio of colloidal sand was greater than 100%.When 10% of the total gel material was added with phosphate tailing powder，the slump of C60 concrete was 230 mm，the strength of 28 d was 64.1 MPa，and the strength of 90 d was 78.6 MPa.At the curing age of 90 d，the new mineral phase hydrotalcite appeared in the cement hardening body mixed with phosphate tailing powder，which was conducive to the strength growth of concrete in the later stage.Phosphorus tail powder could be used as mineral admixture to prepare concrete.

Key words: high-Mg phosphate tailing, mineral admixtures, concrete, poisonous, hydration products