PT Freeport Indonesia operates two parallel concentrators for copper-gold flotation at their Tembagapura operations in Irian Jaya, Indonesia.

 

Overall and Stage Performances

Freeport staff used the assays from the survey samples along with the material balance program BILMAT to obtain a consistent circuit balance. These results are summarized in Table 1. Pyrite recoveries shown in Table 1 were estimated using two assumptions:

(i) %pyrite = 100 – %Insol – %CuSulfide, and
(ii) 43% Cu as the average copper content of the copper sulfide minerals.

Overall, the cleaner circuit produced a final concentrate of 32.1 % Cu and 11.4 % Insol at a copper recovery of 98.3 % from a circuit feed of 10.9 % Cu, which was somewhat better that normal performance. Typical long term average recovery is 96 to 97 %; however, feed rate for this survey was 168 mtph solids (40 minutes nominal residence time) whereas typical feed rate is about 200 mtph (34 minutes).

Gold recovery, at 95 %, was only 3.3 % less than the copper recovery. The ratio of gold to copper recovery was considerably higher in the cleaner columns than in the scavenger columns (0.92 versus 0.83), and the ratio was highest in the cleaner scavenger (mechanical bank) and lowest in the scavenger columns (0.96 versus 0.83).

Size-by-size Performance

63 % of the copper in the final concentrate was obtained through the primary cleaner columns, and 37 % through the scavenger columns. In contrast, 36 % of the Insol in the final concentrate reported via the cleaner columns and 64 % via the scavenger columns. The distribution of copper and Insol between -325 mesh and +325 mesh fractions is summarized in Table 3 for the two column concentrates. As seen in Table 2, the concentrate copper grade decreases with increasing particle size, especially so for the scavenger column concentrate.

The fact that entrainment accounts for only a portion of the insol recovery is consistent with the degree of froth washing that was in place at the time. A material balance around the circuit generates a calculated water flow to the concentrates as shown in Table 4 (this balance assumes that column concentrate is 30% solids, which is a typical value). In both column stages there was more water added than there was water reporting to the concentrate, which is a situation that would tend to minimize recovery via entrainment; however, it would not eliminate entrainment completely, because the water exchange is not perfect.