Effect of Sulfate-Containing Wastewater on the Properties of Phosphogypsum-Based Cemented Paste Backfill
Based on the limitation of mine wastewater treatment process and the large demand for water resources in phosphogypsum backfill process,the feasibility of using sulfate-containing mine wastewater as phosphogypsum backfill water was discussed.Results show that the sulfate present in the wastewater promoted the early hydration of the phosphogypsum-based cemented paste backfill,consequently enhancing its early strength.Specifically,as the sulfate concentration increased from 0 to 30000 mg/L,the 7-day strength of the backfill samples increased from 0.46 MPa to 0.63 MPa,representing a 37%increase.The 14-day strength also exhibited a significant increase from 0.64 MPa to 1.03 MPa,indicating a 61%increase.This can mainly be attributed to the formation of hydration products such as ettringite and C-S-H.However,with the increase of the curing time,the 28-day,60-day,and 90-day strength of the backfill samples reach the highest values at a sulfate concentration of 15000 mg/L.Excess sulfate ions can interfere with the hydration and hardening processes,and the long-term strength of the backfill is affected by the expansion caused by AFt and the recrystallization of Na2SO4 and other influences,resulting in a decrease in the strength of backfill samples.The results can provide a new insight into mine wastewater treatment and phosphogypsum-based cemented paste backfill technology.
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