2.2 Experiment materials
To convenience for the comparison of results, the standard carbonate tablets were made of high purity Devonian limestones from Guilin in Guangxi Zhuang autonomous region. This standard carbonate tablet is the most widely used in China. The results of mainly chemical characteristics analysis of sample rocks show that the limestone contains 55.67% of CaO, 0.43% of MgO, 42.96% of CO2, and 0.66% acid-insoluble substance, respectively. All limestone rocks were cut and sliced into circular standard-sized tablets, with a diameter of 4.0 ± 0.1 cm, a thickness of 0.3 ± 0.02 cm, a surface area of approximately 28.91 cm2, and a weight of 12.45 ± 0.3 g. Each tablet has two holes in the surface that make the tablet closer to the actual dissolution environment. The bodies of these tablets were all polished.
Before the experiment, the standard tablets are cleaning in distilled water three times and then drying in a laboratory oven for 12 h at 103 °C and weighing on the accuracy of 0.1 mg by OHAUS analytical balances (PX224ZH/E). The weighted standard tablets were then labeled and put in a moisture-proof bag for the field experiment. After every experiment period, the tablets retrieved from the field were carefully treated following the same procedure as before the experiment.