This study focused on the flotation behaviour of very coarse quartz particles in the presence of fine silica and alumina, both of which were used as pulp viscosity modifiers. A decrease in the contact angle of the coarse quartz particles, caused by the attachment of fine particles was believed to be the principal mechanism accounting for the noted depression. Only small surface coverage of attached fine particles may dramatically decrease the quartz particle recovery because the flotation behaviour of the coarse particles was very sensitive to particle hydrophobicity, e.g. less than 5% surface coverage is able to decrease the contact of particles from 83 degrees to 81 degrees and causes a decrease in recovery from 60% to 20%. The effect of removing the fine particles from the pulp, by the process known as desliming, on the flotation behaviour of coarse quartz particles was also investigated. The results showed that desliming is beneficial for the recovery of coarse quartz particles. Furthermore, the recovery of coarse quartz particles attached with fine particles can be restored by conducting flotation in high viscosity medium where glycerol was used as the viscosity modifier. (C) 2012 Published by Elsevier Ltd.