Removal of kaolinite particles from water by flocculation with Archachatina marginata snail mucin activated by small amounts of calcium ions

Kaolinite clay material is regularly found in suspensions of mineral tailings and in tropical surface waters. Snail mucin (biopolymer) derives from a liquid waste stream of edible snail meat process. In this study, Archachatina marginata mucin was extracted, characterized and its flocculating activity on kaolinite in water was evaluated in the absence and in the presence of CaCl2. Chemical and amino acid (AA) analyses showed the mucin as protein-polysaccharide biopolymer (82.5% protein). Fourier transform infrared (FTIR) spectroscopy revealed amino, carboxylate, hydroxyl and sulphate functional groups. Zeta potential located the point of zero charge of the mucin at pH 5 and showed it was amphoteric at 5< pH < 8 but anionic at > pH 8. sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) depicted masses >150 kDa as very predominant. Jar tests flocculation on moderate turbidity (105 NTU) suspensions at pH 6 to 8, showed the mucin on its own was poorly flocculating (≤ 20%). Mucin (1 to 2 parts per million [ppm]) associated with calcium ions (40 ppm) gave greatly improved (75 to 90 %) pH dependent flocculation performance in the order pH 7 > pH 8 ?pH 6, while floc settling was pH 8 > pH 7 > pH 6. Mechanism of the flocculation with snail mucin stimulated by Ca2+ was proposed. Key words: Archachatina marginata snail mucin, calcium activation, flocculation, floc settling, kaolinite, protein-polysaccharide biopolymer, water treatment/resource recovery.