Study On The Development And Treating Effect Of Alkali-excited Cementitious Materials For Solidification Of Heavy Metal Contaminated Clayey Soil

At present,widely used cement-based materials and phosphate materials are difficult to meet the repair requirements of high concentration composite heavy metal contaminated industrial sites in China.Therefore,research and development of new environmentally-friendly solidification stabilization chemicals and in-depth study of the effect and mechanism of Stabilized/Solidification?S/S?high concentration composite heavy metals appear especially urgent.In this paper,high concentration Pb,Zn and Cd contaminated soils in Gansu Province were used as the target of repair,and the new Solidification/Stabilization agent was developed.Through theoretical analysis,laboratory test and numerical simulation,a new alkali-activated curing agent SS was obtained.The new alkali-activated curing agent SS repairs the leaching toxicity,strength characteristics,heavy metal transport parameters and heavy metal fixing mechanism of high concentration contaminated soil,and the main conclusions are as follows:?1?According to the screening test based on the sulfuric acid nitric acid method,it can be known that the alkali-activated material mixed with calcium oxide,steel slag and fly ash has the best effect on the stabilization of the white clay,when calcium oxide:steel slag:powder When coal ash=30:56:14,the effect of Solidifying/Stabilized silvery soil is better than other ratios,and the strength increases with the increase of CaO and steel slag content.?2?The factors affecting the leaching toxicity of SS solidified soil were studied by different pH values of leachate,solid-liquid ratio of leachate,initial moisture content of solidified soil and compaction of solidified soil.The study found that the leaching concentration of lead,zinc and cadmium has a concave trend with the change of pH value.When the pH value is less than 5.5 and the pH value is higher than 10.5,the concentration of heavy metal leaching is extremely high,and the concentration of heavy metal leaching is lower in the range of pH 5.5¹0.5.The fluctuation of heavy metal leaching decreases with the increase of liquid-solid ratio?L/S?of leaching solution;the leaching concentration of SS solidified soil changes concavely with the change of water content,and the initial moisture content of solidified soil is 25%.?corresponding to the water-cement ratio of 6.25?,the leaching concentration is the lowest;when the compaction degree is changed,the leaching concentration shows a convex trend with the change of compaction degree,and the leaching concentration is the highest when the compaction degree is 95%.?3?The heavy metal migration characteristics of SS solidified soil were studied by the combination of soil column diffusion model test and numerical simulation.The study found that the concentration of heavy metal in the upper layer of the soil column model increased with time,but the growth rate slowed down.The main physical index of the sample remained unchanged along the depth after the 42d soil column diffusion model test.The concentration of heavy metals in the surface layer increased by 1cm,and the other depths remained basically unchanged.The soil column diffusion model test results combined with the pollute numerical simulation software to calculate the effective diffusion coefficient and partition coefficient of SS solidified soil:the effective diffusion coefficient and partition coefficient of heavy metal Cd are 9.5×10^-13m²/s and 6000mL/g.The effective diffusion coefficient and partition coefficient of heavy metal Zn are 8.5×10^-13m²/s and 15000mL/g.Finally,the influencing factors of effective diffusion coefficient of heavy metals are discussed.?4?The mechanism of SS fixed heavy metals was studied by X-ray diffraction,Scanning Electron Microscopy and Fourier TranSSorm Infrared Spectroscopy.The results show that:SS curing agent curing stabilized heavy metal Pb mainly by physical sealing,physical adsorption and chemical adsorption;SS curing agent curing stabilized Zn mainly by physical sealing,chemical precipitation level physical adsorption and other means;SS curing agent curing stabilization Heavy metal Cd mainly uses physical sealing,chemical precipitation,physical adsorption and chemical adsorption.