| Lead-zinc tailings are solid wastes produced in the beneficiation process of lead-zinc mines.Due to the presence of heavy metals such as Zn,Pb and Cd,the reasonable and safe disposal of them is necessary.Based on the background,the lead-zinc tailings seleceted in this research were obtained from a metallic mine situated in Yunnan,China.After analyzing the basic characteristics of the lead-zinc tailings,alkali-activated coal gangue and blast furnace slag cementitious materials combined with carbon nanotubes were used to solidify/stabilize lead-zinc tailing.Additionally,the stability of solidified bodies in extreme conditions was systematically studied,which provided data support for the harmless disposal of lead-zinc tailings and the application of solidified products.Most of lead-zinc tailings used in the experiment were yellow green powder,and the particle size was distributed in 2.07～295.63μm;The average p H value of lead-zinc tailings was 6.77,weakly acidic,and the water content was 13.50%;The crystallinity of lead-zinc tailings was relatively high,and the main phase components were quartz and calcite,in which the content of quartz was relatively high,and the main chemical components were Si O2,Ca O and Al2O3;Lead zinc tailings were hazardous wastes with leaching toxicity characteristics.The leaching concentration of heavy metal Zn in lead-zinc tailings measured by TCLP method was high,and the leaching concentration of Pb and Cd far exceeded the safety limits.The risk of environmental pollution of heavy metals was at a very high level.Based on the single-factor experiment and response surface experiment,alkali-activated materials were prepared by using coal gangue and blast furnace slag.The experimental results showed that when the waterglass module was 1.06,the alkali content was 13.81 wt%,and the initial 24 h curing temperature was 30℃,the compressive strength of the alkali-activated materials could reach 91.13 MPa（28 d）.The alkali-activated materials prepared under the optimal conditions were used to solidify/stabilize the lead-zinc tailings.It was found that the compressive strength of solidified bodies decreased gradually with the increase of the content of lead-zinc tailings.When the content of lead-zinc tailings was 70 wt%,the solidified bodies still had good mechanical properties（21.68 MPa）.The leaching concentration of heavy metals i.e.Zn,Pb and Cd in the solidified bodies gradually increased with the increase of the content of lead-zinc tailings.The alkali-activated materials could effectively solidify lead-zinc tailings mainly through physical encapsulation,ion exchange and chemical bonding.By comparing the properties of solidified bodies after the disposal of lead-zinc tailings by ultrasonic and carbon nanotube"adsorption-solidification"and"direct solidification",it was found that"adsorption-solidification"treatment reduced the mechanical properties of the solidified bodies and increased the leaching concentrations of heavy metals i.e.Zn,Pb and Cd in the solidified bodies;However,"direct solidification"treatment helped to improve the solidification effect of alkali-activated coal gangue and blast furnace slag cementitious materials on lead-zinc tailings.The compressive strength of the solidified bodies was higher than that of the control groups,and the leaching toxicity of heavy metals was also lower.The solidified bodies showed better stability and had the potential to be used as building materials.The stability of the solidified products in extreme environment was evaluated by their appearance changes,edge length loss,mass loss,compressive strength and leaching toxicity of heavy metals i.e.Zn,Pb and Cd.The results of stability experimental at high temperature showed that the compressive strength varied greatly at different temperatures.The loss rates of compressive strength of solidified bodies exposed at 1100℃for 2 h is more than 47.03%;The leaching concentrations of Zn,Pb and Cd in the solidified bodies at different exposure temperatures were higher than those in the control groups.The results of the environmental stability tests of simulated acid rain showed that the solidified products had different behaviors in mixed acid media with different p H values,and had good acid corrosion resistance.The stability experimental results under the coupling action of sulfate and freeze-thaw cycles showed that the solidified products had good frost and salt resistance（the number of freeze-thaw cycles≤100）. |
PDF Full Text Request