Application of clays to removal of red tide organisms II. Coagulation of different species of red tide organisms with montmorillonite and effect of clay pretreatment

Abstract

Study on the coagulation of four species of red tide organisms (Nitzschia pungens, Skeletonema costatum, Prorocentrum minimum and Noctiluca scintillans) with montmorillonite, and the effect of montmorillonite pretreatment on the coagulation shows that the capability for montmorillonite to coagulate with them is in the order:N. pungens > S. costatum > P. minimum > N. scintillans. The coagulation is discussed from the aspects of the structure, shape, size, movement, habit, etc. of different species and the results are explained theoretically. The experimental results also indicate that the treatment of montmorillonite with acid can enhance its coagulating capability. This is due to the fact that Al(OH₂) ⁺³₆ , exchanged from the clay lattice by hydrogen ion H⁺, forms hydroxy-aluminum polymers on the surface of the montmorillonite. The hydroxy-aluminum polymers positively charge and increase the positive characteristic of the clay surface, and also serves as a bridge between adjacent surfaces of particles. These two functions enhance the montmorillonite's capability for coagulating with the organism cells.