电石渣-稻壳灰固化铜污染土抗压强度及环境特性研究

Compressive strength and leaching characteristics of copper contaminated soil solidified by calcium carbide residue-rice husk ash

为解决铜污染土劣化土体强度及破坏生态环境等问题,提出利用电石渣(CCR)和稻壳灰(RHA)2种固体废弃物对重金属铜污染土进行固化/稳定化。基于无侧限抗压强度试验、毒性浸出试验(TCLP)及微观结构分析,研究不同固化剂配比、龄期及污染物浓度等因素对固化土抗压强度和浸出性影响规律,并分析其微观结构变化。研究结果表明,电石渣−稻壳灰可以显著提升污染土强度和降低铜浸出率,固化前期电石渣−稻壳灰配比为3︰7时固化强度最高,当养护龄期为60 d时,固化剂配比为5︰5时提高固化样力学效果最优,且抗压强度随铜含量增加而先略有升高后大幅降低,高铜含量对固化土强度劣化明显。当初始铜含量为10000 mg/kg以下时,固化后铜浸出浓度低于安全浸出标准。固化剂配比对铜离子固化效果在低初始铜含量下无明显差异,在高初始铜含量下,电石渣和稻壳灰配比为4︰6固化效果更优。经固化剂处理后污染土pH值显著增大,且随着pH升高,浸出浓度呈现先减小后增大的趋势,与氢氧化铜理论溶解度曲线趋势大致相同。电石渣−稻壳灰固化污染土主要产物呈现为硅酸钙水合矿物,有利于降低铜的浸出率,填充土壤孔隙,提高骨架结构,对铜离子具有吸附和离子置换作用。

To solve the problems of deteriorating soil strength and contaminating environment caused by copper contaminated soil,two solid wastes,including carbide slag(CCR)and rice husk ash(RHA),were proposed to solidify/stabilize the heavy metal copper contaminated soil.Based on the unconfined compressive test,toxicity characteristic leaching procedure(TCLP)and microstructure analysis,the laws of different curing agent ratios,ages and pollutant concentrations governing the compressive strength and leachability of cured soil were investigated and its microstructure changes were analyzed.The results show that calcium carbide residue-rice husk ash can significantly improve the strength of contaminated soil and reduce the leaching rate of heavy metal copper.The highest strength occurs when the ratio of calcium carbide residue-rice husk ash is 3︰7 at the precuring stage.When the curing age is 60 days,the curing agent ratio of 5︰5 is optimal in improving the mechanical effect of curing sample.The compressive strength increases slightly with copper content and then decreases significantly,high copper content on the strength of cured soil deterioration is obvious.When the initial copper content is below 10000 mg/kg,the cured copper leaching concentration is lower than the safe leaching standard.There is no significant difference between the curing agent ratio and copper ion fixation effect at low initial copper content,and the fixation effect is better at high initial copper content with a 4︰6 ratio of calcium carbide residue and rice husk ash.The pH of the contaminated soil increases significantly after treatment with the curing agent,and the leaching concentration shows a trend of first decreasing and then increasing with the increase of pH,which is approximately the same as the trend of the theoretical solubility curve of copper hydroxide.The main product of calcium silicate hydrated minerals presented by calcium carbide residue-rice husk ash curing contaminated soil is beneficial to reduce the leaching rate of copper,fill soil pores,improve the skeletal structure,and have adsorption and ion replacement effects on copper ions.