面容比对酸蚀砂岩溶解特性与力学性能的影响

Influence of area-to-volume ratios on dissolution characteristics and mechanical properties of acid-corroded sandstone

为研究静态酸−岩反应体系中,面容比对砂岩溶蚀及劣化特性的影响,选择pH=2、5的盐酸与硫酸溶液为腐蚀环境,通过改变砂岩表面积以设置不同面容比,研究其对砂岩物理化学及力学性质的影响规律,并通过酸岩反应理论,分析面容比对砂岩腐蚀过程中扩散−溶解机制的影响。研究结果表明:在不同面容比条件下,砂岩质量损失率、总阳离子析出量与腐蚀时间均呈幂函数关系,且面容比与溶解速率常数呈正相关,对反应级数影响较小。不同环境下反应级数均小于1,砂岩腐蚀速率随时间逐渐减小。在pH=2、5的盐酸和pH=2硫酸溶液中,不同阳离子析出量N呈现N(Ca^(2+))>N(Na^(+))>N(Mg^(2+))>N(K^(+)),在pH=5硫酸溶液中,则N(Na^(+))>N(Ca^(2+))>N(Mg^(2+))≈N(K^(+))。酸岩反应可概括为扩散控制和化学反应控制2种机制,控制参数均与面容比呈负相关,与溶液pH呈正相关,硫酸溶液中各参数稍大于盐酸溶液中相对应的数值。不同环境下酸岩作用过程均由化学反应主导,且面容比对扩散作用的影响强于化学反应。酸蚀砂岩的力学性能发生劣化,单轴压缩下其破坏过程分为压密、弹性变形、塑性屈服、峰后4个阶段,砂岩峰值强度、弹性模量降低,峰值应变增加,脆性减弱,延性增强,面容比越大,其劣化越严重。整体上,溶液pH越小,面容比对砂岩溶解特性与力学性能的影响越显著,且盐酸溶液对面容比的敏感程度稍强于硫酸溶液。研究结果可为酸化学环境下岩体工程的安全性评估与灾害防治提供理论参考。

To study the effect of area-to-volume ratio on the dissolution and deterioration characteristics of sandstone in the static acid-rock reaction system,the HCl and H_(2)SO_(4)solutions with pH=2 and 5 are selected as corrosion environments,and the different area-to-volume ratios are set by changing surface areas of sandstone.The effects of area-to-volume ratios on the physicochemical and mechanical properties of sandstone are studied.According to the acid-rock reaction theory,the effect of the area-to-volume ratio on the diffusion-dissolution mechanism during sandstone corrosion is analyzed.The res-ults show that the sandstone mass loss rate and amount of substance of total cations are all related to the corrosion time as a power function.The area-to-volume is positively correlated with the dissolution rate constant and has little effect on the reaction order.The reaction order is less than one in different environments,indicating that the sandstone corrosion rate decreases gradually with soaking time.In the pH=2、5 HCl solution and pH=2 H_(2)SO_(4)solution,the amount of substance of cation shows N(Ca^(2+))>N(Na^(+))>N(Mg^(2+))>N(K^(+)),and in the pH=5 H_(2)SO_(4)solution,it is N(Na^(+))>N(Ca^(2+))>N(Mg^(2+))≈N(K^(+)).The acid-rock reaction can be summarized as two mechanisms:diffusion control and chemical reaction control.The two control parameters are negatively correlated with the area-to-volume ratio and positively with the pH value of solutions.The parameter values in the H_(2)SO_(4)solutions are slightly larger than the corresponding values in the HCl solu-tions.The interaction between sandstone and acid in different conditions is dominated by the chemical reaction.The area-to-volume ratio significantly influences diffusion more than the chemical reaction.The mechanical properties of sand-stone are weakened after acid corrosion.The damage of sandstone under uniaxial compression can be divided into four stages:compaction,elastic deformation,plastic yielding and post-peak.The peak strength and elastic modulus decrease,the peak strain increases,the brittleness declines,and the ductility is enhanced.The larger the area-to-volume ratio,the more severe the sandstone deterioration is.Overall,the smaller the pH value of solutions,the more prominent the effects of the area-to-volume ratio on the dissolution characteristics and mechanical properties of sandstone are,which is more ob-vious in the HCl solutions than in the H_(2)SO_(4)solutions.The finding can provide theoretical references for the safety assess-ment and disaster prevention of rock mass engineering under an acidic environment.