Advanced solid-liquid separation for dewatering fine coal tailings by combining chemical reagents and solid bowl centrifugation

Solid-liquid separation to dewater mine tailings is critical to transforming tailings dams that are hazardous to the environment and surrounding communities into safer and sustainable disposal storages by dry stacking and co-disposals. Current tailings dewatering by thickening and filtration has experienced big challenges due to the presence of fine clay minerals with complex surface properties and gelation caused by their swelling characteristics. They retain water in their structure, settle very slowly in thickeners, and pass through filter media during filtration. Here, we have systematically investigated the effect of clay mineral surface chemistry on settling, flocculation, and dewatering using pure clay samples and coal tailings samples. Our results indicate the critical role of clay surface charge in the successful dewatering of the clay samples. A two-step procedure including neutralizing the clay surface charge by salts and then flocculating by salt-resistant flocculants can be significantly effective in the dewatering. The newly-developed dewatering technique by combining chemical reagents and mechanical force of solid bowl centrifugation can deliver successful dewatering outcomes by achieving the required final moisture of dewatered tailings and providing improved water quality for recycling. This paper highlights the importance of clay surface chemistry in controlling clay interactions with chemical reagents, and solid-liquid separation to dewater the clay-rich tailings inherently present in the mining industry.