Gold Recovery by Cyanide Leaching: A Case Study of Small Scale Miners in Tanzania

Abstract

In this study, sodium cyanide leaching technology has been used to recover gold from tailings that are used by Mawelo small

scale miners, located in Chunya district, Mbeya region, Tanzania. The sample collected was sent for analysis of mineralogical

composition and average particle size. The fractions retained on each sieve, which ranged 180 – 500 μm were used in the

leaching experiments. The leaching was implemented using sodium cyanide with concentration in the range of 500 – 1200

ppm, the pH of the reaction mixture was maintained in the range of 10.2 to 10.5 by addition of 5 g of lime (CaO). The retention

time spanned the range of 24 to 96 hours. It was observed that the average particle size, P80 (80% of material passing) of the

sample was 480 μm this was not equal to the liberation size of the sample. In order to increase the gold recovery, grinding of

the sample to 180 μm is required. The mineralogical composition of the sample revealed: gold: 5.85 g/t, copper: 150 ppm,

sulphur: < 0.01 ppm, arsenic: 1.82 ppm, cobalt: 18.25 ppm and nickel: 23. 89 ppm. With 180 μm particle size, the cyanide

dosage in the range of 700-1000 ppm, retention time of 72 hrs, gave a gold recovery of 2.45 ppm which was better than all

parameters studied but represented 42% of the gold recovery in the sample. From this study it is evident that analysis of the

mineralogical composition of the ore and attaining its liberation size are mandatory requirements to effective and efficient

cyanide leaching process.

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