Synthesis and Evaluation of a Submicron Solid Flocculant GCS

Submicron solids laden in drilling fluid as drilling proceeds greatly affect the properties of the drilling fluid, and are thus needed to be removed with flocculants dedicated for the submicron solids. GCS is such a flocculant synthesized with chitosan. The optimum synthetic conditions determined through orthogonal experiment were as follows:3% chitosan, mass ratio of chitosan and crosslinking agent=1:0.28, pH=7. Particle size analysis and sedimentation test were done to evaluate the flocculating effect of GCS, and the flocculating mechanisms of GCS were determined through IR spectroscopy, zeta potential measurement and SEM. It has been found that GCS has good flocculating ability, 95% of submicron kaolinite particles can be flocculated. Compared with other flocculants, such as polyacrylamide, GCS does not viscosify drilling fluids; the sizes of the flocs are narrowly distributed and are thus easy to be separated from drilling fluid. GCS has better flocculating effect in alkaline environment. At higher pH value and GCS concentrations, better flocculation can be achieved, and the flocs become more compact. GCS has -OH, -NH, -C═N and -NH₂ functional groups with which GCS is tightly adsorbed onto the surface of kaolinite particles through these groups, neutralizing the electric charges on the surface of the kaolinite surface, hence increasing the potential of kaolinite particles, thereby coalescing the particles to form flocs.