Clathrate $CO_2$ hydrate formation in soil and soil mineral suspensions

Abstract

First, it was identified the effects of solid surface (soil, bentonite, kaolinite, nontronite, and pyrite) and electrolyte $(NaCl, KCl, CaCl_2, and MgCl_2)$ types on the formation and dissociation of $CO_2$ hydrate in this study. The formation of $CO_2$ hydrate in deionized water was faster than that in aqueous electrolyte solutions. The addition of soil suspensions accelerated the formation of $CO_2$ hydrate in the electrolyte solutions. The hydrate formation times in the solid suspensions without electrolytes were very similar to that in the deionized water. Second, the effect of pH on $CO_2$ hydrate formation in the presence of phyllosilicate mixtures was investigated. Three different pH conditions of phyllosilicate suspensions (Na-montmorillonite-rich and phyllosilicate-rich suspensions) with and without NaCl (3.5%) were prepared and controlled by the addition of an acid or base before the dissolution of $CO_2$. The formation of $CO_2$ hydrate was observed in all phyllosilicate suspensions at 30 bar and 273.4 K. The extent of hydrate formation time appeared to depend on the suspension pHs. The temperature-time plot results showed that hydrate formations were suppressed more in the acidic mineral suspensions than in the basic suspensions. The fastest hydrate formation time can be observed in Na-montmorillonite-rich and phyllosilicate-rich suspensions with and without NaCl at near neutral pH (pH 6~8), followed by basic (~pH 12.0) and acidic (~pH 2.0) pHs. The hydrate formation time can be significantly affected by various chemical species forming under the different suspension pHs. The distribution of chemical species in each mineral suspension was estimated by a chemical equilibrium model, PHREEQC, and used for the identification of hydrate formation characteristics in the suspension. Particle-particle and particle-water interactions may possibly contribute to the delay of hydrate formation. Third, it is observed that there is potential influence of sediment...