Leaching of a Nigerian Refractory Gold Ore Using Aqua Regia

In this research, refractory gold ore from Imogbara deposit in Iperindo area of Osun state Nigeria were collected systematically from various segments of the deposits at different depths to obtain a set of samples that truly represent the deposits. The 50 kg sample collected was subjected to panning in a flowing river to obtain about 1 kg-upgraded sample. The upgraded sample was air dried for few days, pulverized to pass through 300 µm sized sieve and concentrated using shaking table. About 50 g of the gold concentrate was roasted in a furnace operated at temperature of 850°C with a slightly opened door. Reflected light and thin section microscopic observation of the ore sample was carried out. Samples of As-received and roasted gold concentrate from 80% passing 75 µm were leached in a single stage leaching using 32 factorials at temperature of 90°C, with aqua regia prepared from HCl and HNO3 concentration of 1M, 2M and 4M, leaching time 30, 60 and 90 min. The leaching was done using an oven operated at 90°C and a magnetic stirrer operated at 300 rpm at a temperature of 80°C. Leachates from combinations that gave the best-leached result were analyzed using Atomic Absorption Spectrophotometer. Roasted sample leached with high acid concentration of 4M and low time of leaching on a magnetic stirrer operated at a speed of 300 rpm at temperature of 90°C gave the highest percentage of weight loss of 6.58%. The AAS test carried out on the roasted sample leachate confirms gold concentration of 2.2 g/t.