The purpose of this study was to synthesize three anionic dispersants for the formulation of highly concentrated coal-water slurry from cashew nut shell liquid. The performance of the three synthesized dispersants, which are diethanolamine anacardate, triethanolamine anacardate and cardanol-formaldehyde sulfonate, were investigated and compared with a commercial dispersant, sodium lignosulfonate. It was found that cardanol-formaldehyde sulfonate as a new dispersant, synthesized from sulfomethylation reaction of cardanol, formaldehyde and sodium sulfite, was more efficient dispersant for coal-water slurry application than diethanolamine anacardate and triethanolamine anacardate. In the presence of 1.0-1.8 wt% of cardanol-formaldehyde sulfonate, coal-water slurry containing 50% weight fraction of coal could be achieved. Cardanol-formaldehyde sulfonate had a surface activity with the surface tension of 51 mN/m. In addition, the zeta potential was substantially increased with concomitant shift of the progressive dispersant concentration. The slurry stability for a period of as long as 1 month gave below 50% of penetration ratio in contrast to below 30% in the case of bare coal-water slurry. As compared with a commercial dispersant, it was found that cardanol-formaldehyde sulfonate gave similar properties to those of sodium lignosulfonate, within acceptable ranges.
