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CARETECH is a multidisciplinary project supported by the Academy of Finland. The aim of this project is to determine the best natural materials that can be used in desulphurization and carbonation processes using methods from materials science, mineralogy and geology. In this paper, we discuss various properties of limestones, such as the chemical composition, surface structure and define their influence on desulphurization.

Phosphorus (P) is one of the main triggering nutrients responsible for eutrophication which troubles many waters in China. This study was to investigate the influencing factors of limestone (LS) adsorption and establish the parameter of constructed wetland (CW) using LS as the main substrate when treating effluent from a municipal wastewater treatment plant (MWTP) for P removal. First, a series of batch experiments were conducted to study the influencing factors of LS adsorption. Consequently, the P removal efficiency increased with the temperature and was high during the initial 3 h; the efficiency was over 75% even at initial P content 50 mg/L; under 2 mm small LS particle size enhanced the adsorption but the difference was not significant; the efficiency was over 90% when initial pH was below 6.37 and decreased sharply at pH above 8.15; sodium chloride as background electrolyte decreased the adsorption; organic acids including tartaric acid, oxalic acid and citric acid all suppressed the adsorption, and citric acid demonstrated the strongest effect. Then column experiment was conducted to evaluate the effect of the continuous vertical-flow LS bed treating effluent from a MWTP with varying hydraulic retention time (HRT). Over 80 days, the effluent pH was between 7 and 9, and effective running time increased with HRT during which the effluent total P content was below 0.5 mg/L. Short HRT such as 1 h or 1.5 h was recommended for dynamic LS adsorption. It showed that LS was suitable for the substrate in CW for P removal in wastewater advanced treatment.

We saw (Section 4.4) that CO₂ (carbon dioxide) reacts with quicklime (calcium oxide) in water at 25°C, under 1 atm generating calcium carbonate or limestone (CaCO₃). The process is a sequence of two reactions (4.14) and (6.1):

The influence of the C₄A₃$\overline{\text{S}}$ mineral addition on the properties of cement was studied, with industrial Portland cement clinker and laboratory prepared C₄A₃$\overline{\text{S}}$ mineral as based materials. The results indicated that the early strength of cement increased, and the late strength steadily grew with 3-5% of C₄A₃$\overline{\text{S}}$ mineral in Portland cement. For Portland cement with blastfurnace slag, the early and late strengths of cement increased greatly with the addition of 3-5% C4A3S mineral. For the cement in which 5% of clinker was replaced with limestone, the various age strengths of cement increased significantly with addition of 5% C₄A₃$\overline{\text{S}}$ mineral. For the cement in which 5% of the slag or fly ash was replaced with limestone, the strength properties of the cement improved significantly with the addition of 5% C₄A₃$\overline{\text{S}}$ mineral. The addition of C₄A₃$\overline{\text{S}}$ mineral can reduce the initial and final setting times of cement.