Analcime dissolution and silica precipitation in acids : effects of anions

Abstract

Zeolites are a class of aluminosilicates often encountered during acid stimulation of sandstone reserbvoirs. Analcime is one such zeolite, which is found in the reservoirs of Gulf of Mexico in USA and elsewhere. In this work, kinetics of Analcime dissolution in different acids has been investigated using the method of initial rates. The results show that, irrespective of the type of acid used. the dissolution follows Langmuir-Hinschelwood rate law analogous to the Michaelis-Menten equation. Also, the rates at the same acid concentration are similar for all the acids, suggesting that the dissolution rate is dependent only on the [H+] concentration. Anther part of the study deals with polymerization of colloidal silica in very low pH conditions, which is encountered after analcime dissolution. The dissolution yields monosylicic acid, which polymerizes and precipitates out of the solution after a definite lag time. The type of acid used has a strong influence on the lag time and the maximum silica concentration in solution (silica plateau height). The lag time and silica plateau height follow the same trend with different acids and their order of variation is, HNO3>HC1.HBr>HI>H2SO4.