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.