The mineral recovery in a flotation column is the result of the combined effect of two distinct zones: the collection zone, which acts like a first cleaning stage and the froth zone that allows for a secondary cleaning of the minerals entering the froth. In this paper an experimental study of the froth zone behaviour in an industrial flotation column, is presented. The column is rectangular, 2×8 m2 in cross-section and 14m height, and is part of the second copper cleaner circuit of the Colon concentrator at El Teniente, Codelco-Chile. The column produces 30 tph of 32% copper concentrate. A critical dependence of the froth zone recovery with the air rate and to a minor extent with the wash water rate was observed. The average froth depth was about 1 m. The average air holdup along the froth zone was 80 %, for a typical range of gas rate Jg=1.2-1.8 cm/s. The plant water supply was limited and allowed for a superficial wash water rate Jw varying from 0 to 0.1 cm/s, which causes positive and negative bias operation. A semi-empirical model of the froth zone recovery Rf was derived in terms of the operating variables : superficial gas rate Jg, superficial water rate Jw and froth depth Hf, as shown in the following equation, Rf=95exp(-1.44*10-2Hf(1+3Jw)/Jg3) A good agreement was found between the froth model, based on operating variables, and experimentally estimated data of froth zone recovery. The range of the copper recovery in the froth zone observed in the industrial column was 20-70 %, from tests where the global column copper recovery was in the range 40-88 %, respectively. © 1998 Elsevier Science Ltd. All rights reserved.