As a case study to quantify the flotation response, Cu activation of pyrite was examined. Two particle sizes, 106/150 and 37/74 gm (surface area 304 and 901 cm(2)/g), were used. Micro-flotation was performed to determine the rate constant, k, as a function of surface concentration of copper, [Cu](surf). The [Cu](surf) was determined by EDTA extraction and controlled by contact with Cu salt solution or with chalcopyrite and chalcocite particles. The rate constant relative to zero copper, k(Cu)/k(0), followed the same trend against [Cu](surf) for both particle sizes. Chalcocite gave a surface concentration about 40 times higher than chalcopyrite, corresponding to their relative ion production (the b-values in Part I). An estimate of mineral grade likely to cause activation was made assuming the grade was inversely dependent on h and taking the critical grade of chalcocite as 0.1% (Petruk, 2000). This gave a critical chalcopyrite grade of ca. 2%. (C) 2002 Elsevier Science Ltd. All rights reserved.