酸雨作用下碳酸盐岩类文物的溶蚀过程与机理

通过模拟硫酸型酸雨加速侵蚀石灰岩的室内试验,监测了试验过程中试样的质量变化、Ca~(2+)释放量、酸雨pH值变化、计算了H~+消耗速率及试样的表面硬度变化率,对试样的微观结构进行了观察和测量,对比分析了酸雨的淋蚀作用和浸泡作用,根据试验结果讨论了酸雨溶蚀石灰岩的机理,并分析了孔隙特征对石灰岩溶蚀过程的影响。试验结果表明:酸雨的淋蚀作用会溶解石灰岩中的碳酸盐并剥离岩石表面,造成新鲜岩石继续与酸雨作用,加速了石灰岩的质量损失和Ca~(2+)的释放,同时试样的表面硬度和表层微观结构发生相应的改变,但是,溶蚀产物会部分填充石灰岩内的微孔隙和微裂隙,可以有效减缓小尺寸孔隙(0.01μm)的破坏;孔隙特征对酸雨侵蚀石灰岩的过程有重要影响,孔隙率越高,酸雨越容易进入岩石内部并造成破坏;孔隙率一定的情况下,孔隙尺寸越大,酸雨作用的时间和程度会越充分,对石灰岩的破坏也越严重;在相同的试验条件下,试验选取的3种石灰岩中南响堂山石窟石灰岩的抗酸雨侵蚀能力最弱。

Experimental study on carbonate dissolution and erosion effect under attack of simulated sulphuric acid rain

The carbonate rocks are known to suffer from attack of acid rain due to high content of soluble minerals. In order to simulate the process of deterioration of carbonate rocks, the attack of acid rain on different carbonate specimens is accelerated by increasing the acid strength and rainfall intensity. Under simulated sulphuric acid rain, the variations in Ca²⁺ concentration, pH value variation, H⁺ consumption rate of the solution as well as the mass loss are tested. The dissolution mechanism is analyzed and discussed based on the experimental results. Also, the pore characteristics are investigated and analyzed for impact on dissolution process. The results indicate that the dissolution products are removed from rock surface. This leads to mass loss and accelerated removal of the specimens and subsequently changes in micro structures. However, during the dissolution process, parts of micro pores and structures (<0.01 μm) are filled by gypsum crystal, and this can protect the micro pores from further damage. Thus, the porosity and pore characteristics have great influence on the dissolution process. Higher porosity and larger-sized pores are more conducive to the dissolution effect and further erosion. The conclusion may be taken as the scientific support for weathering researches on carbonate rocks and protection of carbonate stone relics.