A complete series of the calcite–otavite solid solutions [(Ca_1−xCd_x)CO₃] were prepared, and their dissolution processes lasting nine months were experimentally investigated. For the dissolution in the N₂-degassed water, the Ca concentrations of the aqueous phases increased up to the steady states after 5040 h of dissolution, and the Cd concentrations of the aqueous phases increased up to the highest values and then decreased gradually to the steady states of 0.017–6.476 μmol/L after 5040 h of dissolution. For the dissolution in the CO₂-saturated water, the Ca and Cd concentrations of the aqueous phases increased up to the peak values and then decreased gradually to the steady states of 0.94–0.46 mmol/L and 0.046–9.643 μmol/L after 5040 h of dissolution, respectively. For the dissolution in the N₂-degassed water at 25 °C, the mean solubility products (log K_sp) and the Gibbs free energies of formation (ΔG_f^θ) were estimated to be −8.45–−8.42 and −1129.65–−1129.48 kJ/mol for calcite [CaCO₃] and −11.62–−11.79 and −671.81–−672.78 kJ/mol for otavite [CdCO₃], respectively. Generally, the log K_sp values decreased non-linearly, and the ΔG_f^θ values increased linearly with the increasing Cd/(Ca+Cd) mole ratio (X_Cd) of the (Ca_1−xCd_x)CO₃ solid solutions. In the Lippmann diagrams constructed for the sub-regular (Ca_1−xCd_x)CO₃ solid solutions with the estimated Guggenheim coefficients a₀ = −0.84 and a₁ = −3.80 for the dissolution in the N₂-degassed water or a₀ = −1.12 and a₁ = −3.83 for the dissolution in the CO₂-saturated water, the (Ca_1−xCd_x)CO₃ solid solutions dissolved incongruently, moved progressively up to the quasi-equilibrium curves for otavite and then along the quasi-equilibrium curve from right to left, approached the solutus curve and finally reached the minimum stoichiometric saturation curve for calcite. The considerably Cd-poor aqueous phases were finally in equilibrium with the CdCO₃-rich solid phases.

In this study, the degradation system of Shewanella oneidensis MR-1 and goethite was constructed with chlorpyrifos as the target contaminant. The effects of initial pH, contaminant concentration, and temperature on the removal rate of chlorpyrifos during the degradation process were investigated. The experimental conditions were optimized by response surface methodology with a Box–Behnken design (BBD). The results show that the removal rate of chlorpyrifos is 75.71% at pH = 6.86, an initial concentration of 19.18 mg·L⁻¹, and a temperature of 30.71 °C. LC-MS/MS analyses showed that the degradation products were C₄H₁₁O₃PS, C₇H₇Cl₃NO₄P, C₉H₁₁Cl₂NO₃PS, C₇H₇Cl₃NO₃PS, C₉H₁₁Cl₃NO₄P, C₄H₁₁O₂PS, and C₅H₂Cl₃NO. Presumably, the degradation pathways involved are: enzymatic degradation, hydrolysis, dealkylation, desulfur hydrolysis, and dechlorination. The findings of this study demonstrate the efficacy of the goethite/S. oneidensis MR-1 complex system in the removal of chlorpyrifos from water. Consequently, this research contributes to the establishment of a theoretical framework for the microbial remediation of organophosphorus pesticides in aqueous environments.