American Journal of Engineering, Technology and Society 2015; 2(6): 162-166 Published online November 10, 2015 (http://www.openscienceonline.com/journal/ajets) ISSN: 2381-6171 (Print); ISSN: 2381-618X (Online) Gold Recovery by Cyanide Leaching: A Case Study of Small Scale Miners in Tanzania Justin William Ntalikwa Department of Mining and Mineral Processing Engineering, School of Mines and Petroleum Engineering, College of Earth Sciences, the University of Dodoma, Dodoma, Tanzania Email address [email protected], [email protected]To cite this article Justin William Ntalikwa. Gold Recovery by Cyanide Leaching: A Case Study of Small Scale Miners in Tanzania. American Journal of Engineering, Technology and Society. Vol. 2, No. 6, 2015, pp. 162-166. 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, P 80 (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. Keywords Mawelo, Small Scale Miners, Cyanide Leaching, Gold Recovery, Retention Time 1. Introduction In Tanzania, extraction of gold from ores by small scale miners takes place in various areas; these include, the Lake Victoria, Lupa, Mpanda and Chunya goldfields. Currently, small scale gold reserves have also been discovered and exploited by artisanal miners in areas of Tanga, Morogoro and Iringa regions [1]. The recovery of gold in these areas is commonly done by using local technology of amalgamation using mercury. Due to environmental and health concerns associated with mercury, a good number of artisanal miners have now started using the technology of leaching by using sodium cyanide. This technology is more efficient in terms of gold recovery as compared to the previous one. However, there are many draw backs associated to the use of this technology by artisanal miners, these include, among others, excessive dosage of cyanide subsequently leading to low profit, and health effects associated with toxicity of sodium cyanide. The chemical element gold, symbol Au, is classified as a noble metal due to its inertness to chemical reactions in non- complex media like aqueous bases. It does, however, react with numerous reagents like a mixture of hydrochloric acid and nitric acid (aqua-regia) and also gold can react with halogens example solution of chlorine to form gold chloride (AuCl 3 ). It belongs to the same group as copper and silver in the periodic table and it is commonly found to be associated with these elements in rocks. In nature, gold occurs predominantly in the native state or as a major constituent of various alloys containing mainly silver, copper, or platinum metals. Several gold and gold-silver tellurides are known, of which the most common are sylvanite (AuAgTe 3 ), calaverite (AuTe 3 ), montbroyite (Au 2 Te 3 ) petzite, krennerite, and nagyagite. The antimonide, aurostibite, (AuSb 3 ), occurs in some auriferous deposits, and there are also argentiferous
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American Journal of Engineering, Technology and Society 2015; 2(6): 162-166
Published online November 10, 2015 (http://www.openscienceonline.com/journal/ajets)
ISSN: 2381-6171 (Print); ISSN: 2381-618X (Online)
Gold Recovery by Cyanide Leaching: A Case Study of Small Scale Miners in Tanzania
Justin William Ntalikwa
Department of Mining and Mineral Processing Engineering, School of Mines and Petroleum Engineering, College of Earth Sciences, the
0.01 ppm, arsenic: 1.82 ppm, cobalt: 18.25 ppm and
nickel: 23. 89 ppm.
(3) With 180 µm particle size, the cyanide dosage in the
range of 700-1000ppm, retention time of 72 hrs, gave a
gold recovery of 2.45 ppm which was much better than
all parameters studied.
(4) Analysis of the mineralogical composition of the ore
and attaining its liberation size are mandatory
requirements for effective and efficient cyanide
leaching process.
166 Justin William Ntalikwa: Gold Recovery by Cyanide Leaching: A Case Study of Small Scale Miners in Tanzania
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