Study On Preparation Of Glass-ceramics From Lead-zinc Tailings And Harmlessness Of Heavy Metals

In this paper,lead-zinc tailings were used as the research object,and high value-added glass ceramics were prepared by adding a small number of chemical agents.The influence of Ca O/Si O₂ ratio of basic glass on the crystallization and properties of glass-ceramics was studied while the effects of crystallization temperature,crystallization time and heating rate on the structure of crystal,physical properties and chemical corrosion resistance of glass-ceramics were further explored by a series of analysis methods basis of the optimal Ca O/Si O₂ ratio of basic glass.What's more,the solidification/stabilization effect of glass-ceramics on heavy metals was also discussed.The main conclusions are as follows:(1)By adjusting the ratio of lead-zinc tailings and chemical reagents,the basic glass ingredients with different Ca O/Si O₂ ratio were prepared.Glass-ceramics were successfully prepared by high temperature melting,water quenching and sintering method.When the basicity increases from 0.25 to 0.5,the crystallization peak first moves to the direction of low temperature,then to high temperature.The crystal phase in the microcrystalline vitreous is mainly composed of albite,diopside and gehlenite.With the increase of the Ca O/Si O₂ ratio,the changes of compressive strength and bulk density of glass ceramics are similar.The weight loss rate of glass ceramics in acid is greater than that in alkaline solution.The best comprehensive properties of glass ceramics occurred when the basicity is 0.45,which the density was 2.93 g/cm³,the compressive strength was 182.64 MPa,the weight loss in acid solution was 2.26%,the weight loss in alkaline solution was 1.65%,and the content of lead-zinc tailings is70.86%.(2)The experimental results of the influence of crystallization temperature on the comprehensive properties of glass ceramics show that with the increase of crystallization temperature,the types of crystalline phases of glass ceramics have not changed,but the crystallinity has increased,and the peak value is clear and sharp.The diffraction peaks of albite,diopside and gehlenite crystals change obviously,indicating that the relative contents of the three have changed.The change of compressive strength and alkali corrosion resistance of glass ceramics is positively correlated with the increase of crystallization temperature.With the increase of crystallization temperature,the bulk density and acid corrosion resistance of glass ceramics increase first and then decrease.The compressive strength reaches the maximum value of 184.41MPa at the crystallization temperature of 1036°C,and the alkali corrosion resistance of the glass ceramics reaches the maximum value of 98.51%.When sintered at 996°C,the density and acid corrosion resistance of the glass ceramics are the highest,which are 2.93g/cm³and 97.81%respectively.(3)With the increase of crystallization time from 60min to 180min,the crystallinity of the glass ceramics increases gradually,and the diffraction peak intensity of the main crystal phases increases first,then decreases,and finally increases.The highest value of185.7MPa is obtained at 150min,which may be related to the microcracks produced by the glass ceramics.The change of bulk density was positively correlated with the increase of crystallization time.The highest value of 2.93g/cm³ was obtained at 180min sintering.With the increase of crystallization time,the acid resistance of the glass ceramics gradually increased,and the alkali resistance first increased and then decreased,and reached the maximum value when the crystallization time was 180min and 150min respectively,and the acid corrosion resistance and alkali corrosion resistance reached the maximum,97.87%and 98.37%respectively.(4)The intensity of diffraction peak is the strongest when the heating rate is3°C/min,and the crystallinity is the highest.With the increase of heating rate,the compressive strength and bulk density of the glass-ceramics samples gradually decrease,which indicates that slow heating can ensure the slow growth and close development of the crystal,and then improve the mechanical properties of glass-ceramics.When the heating rate is 12°C/min,the compressive strength is the lowest,which is 178.09 MPa,and the bulk density is 2.89g/cm³,which is also the lowest value.In addition,significant difference analysis shows that the change of heating rate has little effect on the chemical corrosion resistance of glass ceramics.(5)The toxicity test of heavy metal leaching by TCLP method shows that the concentration of heavy metals in the leaching solution is far lower than the threshold value stipulated by the United States Environmental Protection Agency(USA EPA),which has good environmental safety.The calculation results of heavy metal leaching rate show that glass ceramics have the best curing effect on Zn,followed by Mn and Pb.With the increase of crystallization temperature,the curing effect of glass ceramics on Zn and Pb is better and better,while Mn is better and worse at first.With the increase of crystallization time,the leaching rates of Mn and Zn decreased,while that of Pb decreased at first and then increased,indicating that Pb participated in the formation of network or was wrapped in the structure most at 120min.With the increase of heating rate,the change of heavy metal leaching rate is consistent,that is,the faster the heating rate is,the worse the solidification effect is.When the heating rate is 12°C/min,the leaching rates of Zn,Mn and Pb are the highest,which are 7.56%,22.36%and 34.47%,respectively,which is fundamentally related to the poor crystal development caused by too fast heating rate.For heavy metals,the solidification effect of Zn and Mn is the least affected by the basicity of basic glass,and that of Pb is the least affected by crystallization time.