Reaction Kinetics of Sodium Bentonite with Different Acid Systems: An Experimental Study

Abstract

Discovering the characteristics of the reaction kinetics of acid systems (hydrogen fluoride (HF), hydrochloric acid (HCl), and CH3COOH) at different concentrations with sodium bentonite can provide experimental support for optimising formulations used in removing plugs through acidification. By utilising a spectrophotometer and acid-base titration, changes in contents of Si, Al, and H+ concentration when sodium bentonite reacted with different acid systems (HF, HF, HCl, and HF and CH3COOH) at different concentrations (5%, 10%, and 15%) for different reaction times (1, 2, 4, 8, 12, and 24 h) at 45°C were measured. Based on this, a reaction kinetics model of H+ was fitted and reaction mechanisms of HF with sodium bentonite after adding HCl and CH3COOH were analysed. The results demonstrated that the rate of dissolution of Al was high and the reaction reached equilibrium in 1 h. Si showed a fast dissolution rate in the acid solution containing HF. In an HCl + HF + CH3COOH acid system, at a concentration of 15%, the greatest dissolution occurred, with a more stable dissolution rate and longer reaction time. Among the three acids tested, it was HF that mainly reacted with sodium bentonite, while the other two acids had weak reactions therewith. In the acid system containing HF, HF molecules reacted with sodium bentonite, rather than other forms, such as H+, F−, and HF2−. The addition of HCl could promote the reaction, while CH3COOH inhibited the reaction. The research results provide experimental support for optimising the formulation of such acid solutions.