Experimental Study On Using Additives For Drag Reduction And Harmful Ion Curing In Phosphate Tailings Cemented Filling

In recent years,backfill mining method has received widespread attention and been applied in many mines due to its environmental and economic benefits.When the tailings are used as filling materials for underground filling,there are some problems such as environmental pollution and high slurry transportation cost,which restrict the popularization and application of filling mining method.Experimental study on using additives drag reduction and harmful ion curing for phosphate tailings cemented filling has great significance to protect the mine environment,reduce the cost of filling,improve the recovery rate of resources,and realize the green exploitation of mine resources.This paper analyzed the characteristics of filling materials of phosphate tailings,fly ash,cement and phosphate tailings filling slurry.Through the bleeding test and leaching test,determined the curing agent and dosage.The method of fluidity,divergence and L tube were used to menstruate the flow behavior of the filling slurry,and then determined the appropriate drag reduction agent and dosage.The main conclusions are as follows.The filling slurry bleeding was determined,found that the concentration of SO₄^2-was 2691 mg/L and F^-was 5.1 mg/L,which belongs to the class V quality standard of ground water,the bleeding rate was 5.1%.There will pollute the underground environment.In this paper,CaO,PAC and PAM（Cationic）were used to curing these,the three kinds of curing agents were used for bleeding test and leaching test.Filling slurry water was determined when the dosage of curing agent was 0.4% PAC and 4% CaO,found that the concentration of SO₄^2-was 335 mg/L and F^-was 1.9 mg/L which belongs to the class Ⅳ quality standard of ground water,and low bleeding rate was 1.7%;The content of SO₄^2-in the leached water is lower than 150 mg/L and F^-is less than 1 mg/L,which belongs to the classⅡ quality standard of ground water.In order to improve the fluidity of slurry,polycarboxylate-type drag reduction agent,naphthaldehyde-type drag reduction agent and citric acid were used for drag reduction test.The results showed that the best effect of drag reduction is use 1.2% polycarboxylate-type drag reduction agent.Divergence,viscosity and shear stress were improved by 47.40%,56.47%,55.56%,and 57.81%.The bleeding rate was 1.5%,the concentration of SO₄^2-and F^-were 280 mg/L and 2.0 mg/L which belongs to the class Ⅳ quality standard of ground water,it could meet the requirements of transportation drag reduction and harmful ions curing.Citric acid has good retarding effect on the filling slurry.When the citric acid content is 2.5%,the hourly loss rate of the fluidity and divergence were 2.91% and 1.37%.Citric acid can be considered added to filling slurry when long distance slurry transportation,which can maintain the flow performance for a long time.Adding a right amount of polycarboxylate-type drag reduction agent,naphthaldehyde-type drag reduction agent and citric acid can improve the compressive strength of 28 d.However,if the drag reducing agent was too much,the compressive strength of the backfill will decrease.It is concluded that the ideal combination additive was 4% CaO,0.4% PAC and 1.2% polycarboxylate-type drag reduction agent.The filling slurry has a better flow performance,the viscosity was 3.36 Pa·s,and the yield stress was 2.7 Pa,it has a less conveying resistance,the 28 d compressive strength of the filling body was 3.32 MPa,it can meets the requirements of underground pressure,and it also has a little pollution to the groundwater,the concentration of pollutants in the leaching water of the filling body is low,which belongs to the classⅡquality standard of ground water,and meeting the requirements of filling underground water quality.