The effects of water recycling on flotation at a North American concentrator

Abstract Due to environmental reasons and water shortage, concentrators have to increase water recirculation in the plant. The water originates from different sources, and depending on their origins, the water chemistry varies from stream to stream. Water chemistry has many significant impacts on flotation, beneficial or non-beneficial. Flotation tests have been conducted using process water (originates from tailings treatment facilities and is clean water that can be released to the environment) and thickener tank overflow water obtained from a North American concentrator. The concentrator would like to increase the recirculation of the thickener tank overflow water and reduce process water consumption. In this work, the flotation results between process water (PW) and thickener tank overflow water recirculated at various degrees were compared. Reverse osmosis (RO) at different degrees of recirculation (0%, 20%, 40%, 60% and 80% RO) was used to simulate water thickener tank overflow water recirculation. The results showed that higher pyrrhotite recoveries were obtained when thickener tank overflow water recirculated (0%, 20%, 40%, 60%, and 80% RO) was used compared to that obtained with process water. However, the pyrrhotite recovery did not increase between 0% and 20%, 40%, 60% and 80% RO. Relative to the process water, the higher pyrrhotite recovery using thickener tank overflow water at various degrees of recirculation did not appear to have been caused by a higher relative proportion of activating species on grain surfaces. Most likely, the higher pyrrhotite recovery in the thickener tank overflow water (0%, 20%, 40%, 60%, and 80% RO) relative to that of process water was due to higher bubble surface area flux (smaller air bubbles) caused by the higher total dissolved solids (TDS) relative to that of process water. Non-sulphide gangue (Ga) recovery was similar for all tests and was mainly due to water entrainment. The nickel and copper recoveries increased at 60% and 80% RO relative to that of process water, probably due to the higher bubble surface area flux generated by the higher total dissolved solids (TDS) in the recycled thickener tank overflow water. Pentlandite (nickel-bearing mineral) grains from the 80% RO and process water samples showed similar proportions of gangue species (e.g. calcium and magnesium) on their surfaces. However, nickel and iron oxide species were slightly higher on pentlandite from the 80% RO sample relative to the process water. The marginally higher amount of hydrophilic oxidative species on pentlandite from the 80% RO could perhaps account in part for the difference in flotation kinetics observed between the samples.