Artisanal and small-scale gold mining (ASGM) faces challenges in accessing capital, technology, and responsible practices, hindering sustainable operations and contributing to environmental and health impacts from mercury use. This study evaluated optimizing direct smelting of gold concentrates as an alternative to mercury amalgamation for efficient and responsible production. 50 kg of ore from Nholi mine was concentrated using a Knelson concentrator and analyzed (XRF, fire assay with AAS, XRD). Response surface methodology with a face-centered composite design investigated smelting temperature (1100–1400 °C), duration (30–90 min), and concentrates-to-flux ratio (1:1–3:1) effects. The impact of sulfide concentration (pyrite varied 6.7–48%) on gold recovery was explored. Low-sulfide concentrates associated with pyrite and sphalerite yielded best recovery (>80%) at 1250 °C for 90 min with 2:1 concentrates-to-flux ratio. Direct smelting with ≤6.7% sulfide enabled over 87% gold recovery, facilitating responsible ASGM production.
KinyondoAHugginsC. Centres of excellence’ for artisanal and small-scale gold mining in Tanzania. The Extr Industri Soc2020; 7: 758–766.
2.
URT. United Republic of Tanzania Parliamentary speech of honourable Doto Mashaka Biteko, minister of minerals reporting to the parliament the budget estimate for the financial year 2020/2021. Dodoma: Parliament of Tanzania, 2020.
MutagwabaWTindyebwaJBMakantaV, et al.Artisanal and small-scale mining in Tanzania–evidence to inform an action dialogue. London: IIED, 2018.
5.
Intergovernmental Forum on Mining. Global trends in artisanal and small-scale mining (ASM): a review of key numbers and issues. Winnipeg: IISD, Canada, 2017.
6.
AppelPWUNa-OyLD. Mercury-free gold extraction using borax for small-scale gold miners. J Environ Protect2014; 5: 493–499.
7.
StylesMTAmankwahRKAl-HassanS, et al.The identification and testing of a method for mercury-free gold processing for artisanal and small-scale gold miners in Ghana. Int J Environ Pollut2010; 41: 289–303.
8.
VeigaMMAngeloci-SantosG. Review of barriers to reduce mercury use in artisanal gold mining. The Extr Industri Soc2014; 1: 351–361.
9.
Angeloci-SantosG. Myths and realities in artisanal gold mining mercury contamination. Dissertation, University of British Columbia, Vancouver, 2013.
10.
KeaneSBernaudatLDavisKJ, et al.Mercury and artisanal and small-scale golding mining: review of global use estimates and considerations for promoting mercury-free alternatives. Ambio2023; 52: 833–852.
11.
CordyPVeigaMMSalihI, et al.Mercury contamination from artisanal gold mining in Antioquia, Colombia: the world’s highest per capita mercury pollution. Sci Total Environ2011; 410: 154–160.
12.
MartinezGRestrepo-BaenaOJVeigaMM. The myth of gravity concentration to eliminate mercury use in artisanal. The Extr Industri Soc2021; 8: 477–485.
ZolnikovTROrtizDR. A systematic review on the management and treatment of mercury in artisanal gold mining. Sci Total Environ2018; 633: 816–824.
15.
AbbeyCENarteyRSAl-HassanS, et al.Direct smelting of gold concentrates, a safer alternative to mercury amalgamation in small-scale gold mining operations. American Int J Res Sci Tech Eng Math2014; 7: 74–179.
16.
AmankwahRKStylesMTNarteyRS, et al.The application of direct smelting of gold concentrates as an alternative to mercury amalgamation in small-scale gold mining operations in Ghana. Int J Environ Pollut2010; 41: 304–315.
17.
StoffersenBKøster-RasmussenRCardeñoJIC, et al.Comparison of gold yield with traditional amalgamation and direct smelting in artisanal small-scale gold mining in Uganda. J Health Pollut2019; 9: 191205.
18.
AppelPWNa-OyL. The borax method of gold extraction for small-scale miners. J Health Pollut2012; 2: 5–10.
19.
YangTXieBLiuW, et al.Enrichment of gold in antimony matte by direct smelting of refractory gold concentrate. JOM2018; 70: 1017–1023.
20.
QinHGuoXTianQ, et al.Recovery of gold from sulfide refractory gold ore: oxidation roasting pretreatment and gold extraction. Miner Eng2021; 164: 106822.
21.
MarsdenJOHouseCL. The chemistry of gold extraction. Colorado, USA: SME, 2006.
22.
TemboMMMdeeOJ. Analysis of ore hand-crushed size distribution for grinding process in the artisanal and small-scale gold mines production: a case study of nholi mine, bahi district. Tanz J Eng Technol2022; 41: 95–105.
23.
MacheyekiASDelvauxDBatistMD, et al.Paleoseismic investigations along the Bubu fault, Dodoma-Tanzania. Tanz J Sci2012; 38: 138–154.
24.
Tanzania Geological Society. Annual meeting and workshop: Book of abstract, Dodoma, https://www.academia.edu/en/69368983 (2018, accessed 17 March 2023).
WangHJFengYLLiHR, et al.Simultaneous extraction of gold and zinc from refractory carbonaceous gold ore by chlorination roasting process. Trans Nonferrous Metals Soc2020; 30: 1111–1123.
29.
AmankwahRKOfori-SarpongG. Microwave roasting of flash flotation concentrate containing pyrite, arsenopyrite and carbonaceous matter. Miner Eng2020; 151: 106312.
30.
OmranianSRHamzahMOValentinJ, et al.Determination of optimal mix from the standpoint of short term aging based on asphalt mixture fracture properties using response surface method. Constr Build Mater2018; 179: 35–48.
31.
WangGXieSLiuS, et al.Bio-oxidation of a high-sulfur and high-arsenic refractory gold concentrate using a two-stage process. Miner Eng2018; 120: 94–101.
32.
MontgomeryDC. Design and analysis of experiments, 5th ed. New York: John Wiley and Sons, Inc., 2001.
OrabyEAEksteenJJTandaBC. Gold and copper leaching from gold-copper ores and concentrates using a synergistic lixiviant mixture of glycine and cyanide. Hydrometallurgy2017; 169: 339–345.
36.
AsamoahRK. Specific refractory gold flotation and bio-oxidation products: research overview. Minerals2021; 11: 93.
37.
LiWJLiuSSongYS, et al.Comprehensive recovery of gold and base-metal sulfide minerals from a low-grade refractory ore. Int J Miner Metall Mater2016; 23: 1377–1386.
38.
HeYHuXZiF, et al.Solidification of sulfur and arsenic in gold concentrate and leaching of the gold by thiosulfate. Asia-Pacific J Eng2020; 15: e2396.
39.
LiuXLiQZhangY, et al.Simultaneous removal of S and As from a refractory gold ore in a single stage O2-enriched roasting process. Metall Mater Trans B2019; 50: 588–1596.
40.
ErdeneboldUSungCMWangJP. Gold recovery from flotation concentrate from gold mine tailings using dissolve smelting. J Min Metall B: Metall2019; 55: 343–349.
