Study On Leaching Characteristics And Cure Of Heavy Metals From Sulfide Ore Tailings Under Simulated Acid Rain

There are a large amount of sulfide ore tailings in China,and sulfide minerals in the tailings are prone to oxidation reaction in the air,which will cause the acidic wastewater and the release of a large number of heavy metals.The release of heavy metals from the tailings will seriously pollute the surrounding environment and threaten human health and safety.In order to control pollution caused by heavy metals in sulfide ore tailings from fountainhead,two kinds of lead-zinc mine tailings(F and YD)and three kinds of tin polymetallic mine tailings(CH1,CH2 and CH3)with different weathering degrees were used to investigate the leaching law of heavy metal ions from the metal sulfide mine tailings,and the sodium diethyldithiocarbamate modified bentonite(DDTC-Mt)was applied to cure the heavy metals in the tailings.The effects of p H value of simulated acid rain,temperature and time on the cure of heavy metals in tailings were systematically studied.Meanwhile,the cumulative release amounts of heavy metals in tailings before and after curing were fitted with kinetic equations,and the curing mechanism of heavy metals in tailings by modified bentonite was discussed,which could provide theoretical basis for the treatment of heavy metal pollution in the tailings.The main research results of this paper are as follows:(1)The main minerals in the tailing sediment(CH1),fresh tailing(CH2)and weather tailing(CH3)were quartz,calcite and pyrite,while the main minerals in the lead-zinc tailings(F and YD)were quartz,sphalerite and pyrite.Compared with four heavy metals in the five tailings,the total contents of As were more than 8000 mg/Kg,and greater than those of the other heavy metals,while the total contents of Mn were relatively lower.The tailings of CH1 and YD had high acid producting potential,CH2 and F had medium acid producting potential,CH3 had weak acid producting potential.The main occurrence modes of Mn and Pb in the five kinds of tailings were exchangeable state and primary sulfide state,and the potential migration abilities were very strong;the main occurrence modes of As were residual state and primary sulfide state,and the main existing forms of Zn were residue state,organic state and primary sulfide state,and the potential migration ability was relatively weak.(2)The cumulative release amounts of As,Pb,Zn and Mn in five kinds of tailings increased with the increase of the release time.The release progress could be divided into two stages,a faster stage and a slower stage.The cumulative release amounts of Mn,Zn and As in the tailing(F)within 72 h were significantly higher than those of the other four tailings,whereas the cumulative release amount of Pb was lower than the others.With the increase of simulated acid rain p H value and temperature,the release amount of Mn and Zn in the tailing(CH1)decreased,whereas Mn,Zn and Pb in the tailings(CH2,CH3 and YD)changed little.Moreover,the release amount of As in the tailings(F and YD)increased with the temperature increasing.In addition,the release amounts of Mn and Zn in the tailings CH1,CH2 and CH3 increased in the following order: CH1 > CH2 > CH3,which was consistent with the acid producing potential of the tailings.(3)Under the conditions of the reaction temperature of 40?,the reaction time of 2 h and the p H value of the simulated acid rain of 4.5,the cure rates of Mn in the tailings CH1,CH2 and CH3 after adding DDTC-Mt increased in the following order: CH1 > CH2 > CH3,which was consistent with the acid producing potential of the tailings.For the tailings F and YD,the cure rates of Mn and Pb followed the order: YD > F,which was consistent with the acid producing potential of the tailings as well.After adding DDTC-Mt,the cumulative release amount of Zn,Mn,As and Pb in the five tailings increased with the increase of the release time.The cumulative release amount of Mn,Zn and Pb increased rapidly in 0-8 h,and then increased slowly and tended to be stable after 8 h.The simulated acid rain p H value has little effect on the release amount of heavy metals in the DDTC-Mt cured tailings.However,the p H value of the tailings leaching solution after adding DDTC-Mt was higher than that of the simulated acid rain initial p H value and the tailings leaching solution without adding DDTC-Mt.After adding DDTC-Mt,the temperature had relatively greater effect on the release amount of Mn,Zn in the tailing(F)and As in the tailing(CH3),whereas it had less effect on the release amount of four heavy metals in the other tailings.The curing effects of four heavy metals partly increased with the increase of the dosage of DDTC-Mt.When the used amount of DDTC-Mt was 3.00 g,the cure rates of Mn and Zn in five kinds of tailings were higher than 80%,and the cure rates of four kinds of heavy metals in tailing F reached 100%.(4)The secondary kinetic equation fitted well with the release process of four heavy metals in two kinds of lead-zinc ore tailings(F and YD)without adding DDTC-Mt as well as the tailings(F,CH1,CH2 and CH3)after adding DDTC-Mt.While the release process of four heavy metals could be better described by the Elovich equation and the double constant equation in the tailings(CH1,CH2 and CH3)without adding DDTC-Mt.The release process of four heavy metals in the tailing(YD)after adding DDTC-Mt could be well fitted with the parabolic diffusion equation.(5)The X-ray diffraction(XRD)and scanning electron microscope(SEM)results showed that the main mineral of the five tailings before and after curing was quartz,while the contents of the other minerals such as sphalerite,chalcopyrite and calcite decreased.After 72 h curing,the five kinds of tailings surface could be covered by DDTC-Mt,which would inhibit the release of heavy metals from the tailings and partially adsorb the released heavy metals.