Study On The Influencing Factors Of The Properties Of Cemented Paste Filling Materials In Copper Mine Tailings

At present,how to deal with abandoned tailings is a key issue.In addition to environmental hazards,safety risks caused by tailings accumulation are particularly important.The preparation of Cemented paste backfill(CPB)with cementing materials is an important method for tailings treatment at present.The preparation of Cemented paste backfill with solid waste can not only protect the environment,but also benefit the reuse of resources.In this paper,copper tailings as aggregate,alkali activated slag as filling cementing material(chemical pure NaOH,CaO and strength grade 42.5 ordinary Portland cement as alkali activator),and mixed with a certain proportion of water to prepare cemented paste backfill.Using single factor variable method and contrast test method(cement as contrast cementitious material),The influence of factors such as the type and content of alkali,the content of double gypsum and alkali,the nature and content of gypsum and the content of cementing material on fluidity and unconfined compressive strength of copper tailings cemented paste backfill was systematically studied in the laboratory,and the formation mechanism of macroscopic properties was studied by microscopic analysis(XRD,SEM).The main research contents and conclusions are as follows:(1)The influence of alkali types and dosage on the performance of copper tailings cemented paste backfill was studied.The main results are as follows:For the fluidity of CPB slurry,the initial fluidity and 1h fluidity of CPB-NAS slurry have little change when the NaOH content in the activated slag cementing material(NAS)increases from 2%to 10%.When the content of CaO in CAS increased from 2%to 10%,the initial fluidity of CPB-CAS slurry decreased slightly and had little change in 1h.When the content of alkali(OPC)in cement-activated slag cementing material(PAS)increases from 2.5%to 20%,the initial fluidity and 1h fluidity of CPB-PAS slurry decrease obviously.As for the compressive strength of CPB,the compressive strength of CPB(from 3d to 28d)increased with the increase of alkali content in alkali-activated slag cementing material,but the compressive strength of CPB from 14d to 28d decreased when NaOH content in NAS reached 10%.When the content of alkali in alkaliactivated slag cementing material is low,the 3d compressive strength of CPB is low.XRD analysis shows that the hydration products of NAS,CAS and PAS are amorphous(calcium silicate aluminate hydrate(C-A-S-H),sodium silicate aluminate hydrate(NA-S-H)gel and its microcrystallization)and hydrotalcite crystalline phase.CAS and PAS also have Ca(OH)2 crystalline phase when the alkali content is higher.SEM analysis shows that with the increase of the content of alkali activator,the hydration products increase and the microstructure becomes more dense,leading to the increase of compressive strength.The conclusion is that considering the fluidity and compressive strength of CPB slurry,the alkali-activated slag cementing material contains less NaOH and CaO than cement,so it is more environmentally friendly.(2)The influence of the dosage of double mixing gypsum and alkali on the performance of copper tailings cemented paste backfill was studied.The main results are as follows:the mixing amount of double gypsum(CPG)and alkali has a slight effect on the fluidity of CPB slurry of copper tailings and is favorable.The 28d compressive strength of CPB-N6AS-CPG20 doped with gypsum(6.2MPa)is 87.9%higher than that of CPB-N6AS-CPG0 doped with gypsum(3.3MPa).Microscopic analysis shows that the hydration products of NAS-CPG are amorphous phases[calcium silicate aluminate hydrate(C-A-S-H)and sodium silicate aluminate hydrate(N-A-S-H)gel and its microcrystallization]and crystalline phases[ettringite(AFt),dihydrous gypsum(CaSO4·2H2O),hydrotalcite,etc.].The conclusion is that the content of 20%gypsum and 6%alkali(NaOH)in alkaloid-activated slag cementing material is an optimal matching relationship,and the CPB prepared from copper tailings can obtain the highest compressive strength.(3)The influence of gypsum properties on the performance of copper tailings cemented paste backfill was studied.The main test results were as follows:the slurry fluidity prepared by wet grinding phosphogypsum of ball mill(wet grinding time:0min,30min and 60min,respectively,was described as PG,30MPG and 60MPG)was relatively high,and the fluidity of CPB-CAS-MPG decreased with the increase of wet grinding time.The 28d compressive strength of CPB-C2AS-CPG20,CPB-C2AS-PG20,CPB-C2AS-30MPG20 and CPB-C2AS-60MPG20 prepared by mixing gypsum with different properties is 7.9MPa,4.1 MPa,7.3MPa and 7.4MPa,respectively.The hydration products of slag cementing materials excited by different properties of gypsum and CaO are mainly C-A-S-H,AFt and CaSO4·2H2O.SEM showed that CPB prepared by wet grinding of phosphogypsum for 30min(including 60min)and calcined phosphogypsum had similar microstructure,so the compressive strength of the three was similar at 28d.Conclusion phosphogypsum can be used instead of calcined phosphogypsum after wet grinding for 30min.(4)The influence of cementing material content on the performance of copper tailings cemented paste backfill was studied.When the cementing material content is 7%,the 28d compressive strength(7.9MPa)of CPB-C2AS-CPG20 increases by 192.6%compared with that of contrast filling body(CPB-OPC).The 28d compressive strength(6.2MPa)of CPB-N6AS-CPG20 increased by 129.6%.Meanwhile,compared with OPC,the cost of N6AS-CPG20 is 68.8%of that of OPC,and that of C2AS-CPG20 is 54.4%of OPC.The conclusion is that the double-mixed gypsum and alkali-activated slag cementing materials(including N6AS-CPG20 and C2AS-CPG20)can replace ordinary Portland cement(OPC)for the preparation of mine tailings cementing paste filling materials with high efficiency and environmental protection.