Effect of carboxymethylcellulose and starch depressants on recovery of filler and fines in tertiary flotation

Abstract

Yield loss in state-of-art deinking processes for newsprint is usually 15%–20%. Economic and environmental concerns associated with reject handling point to a need to improve yield. This paper describes a study conducted to determine whether it is possible to recover fillers and fiber fines from flotation froth reject of an old newsprint/old magazine processing mill by refloating froth with and without the use of depressants. The recovery of approximately 10%–15% of material was observed without the use of additional flotation chemicals in the reflotation stage. Carboxymethylcellulose (CMC) was observed to be a functional depressant that enhanced fiber fines recovery in particular and, to some extent, china clay recovery but lowered calcium carbonate recovery. The recovery increased to 20%–30% with a dosage of approximately 1 kg CMC/ton of pulp. In addition, starch had a depressing effect, but this effect was weaker than that of CMC, even with much higher dosages.