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Microanalysis study of Al-Amar rock and leaching behavior of its tailings for recovery of gold and silver

Mahmoud M. H. H., Awad H. M., Altalhi T.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 2

527--537

EN

Some Saudi gold ores, such as that at Al-Amar mine, suffer from low leaching efficiency using the toxic cyanidation process. Only about 60% of the gold and 26% of the silver in the feed ore can be extracted at 0.2% CN– after 24 h and the rest percentages of these metals remained in leaching residues (tailings). These tailings contained 1.1 ppm Au and 4.3 ppm Ag. Reprocessing of tailings serves both for economic and environmental reasons. A petrography analysis of the mineral constituents indicated that the rock samples consisted primarily of sphalerite, chalcopyrite, pyrite and galena in decreasing order of abundance. An electron probe microanalysis quantitatively showed that gold and silver were finely distributed in the grain boundaries and within sphalerite, chalcopyrite, pyrite, and quartz. The dissemination of gold and silver in these hard minerals may be the main reason for their low recovery by cyanidation. Open air roasting of the tailings can release amounts of the disseminated gold and silver which can be extracted during leaching with the harmless thiosulfate ion S2O32–. After studying the different parameters, we found that the maximum possible extraction of gold and silver from the tailings roasted for 2 h at 400°C reached about 50% at 0.2 M ammonium thiosulfate, 0.3 M ammonium hydroxide, solid–liquid ratio ½ for 24 h. These achievements represent a possible exploitation of the accumulated 1.65 million Mg tailing waste containing significant amounts of gold and silver valued at about $73 million.

2

Gold leching from a Saudi ore by the nonpolluting thiosulfate process

Mahmoud M. H. H., Awad H. M., Elhabib O. A.

Physicochemical Problems of Mineral Processing

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2015

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Vol. 51, iss. 1

59--72

EN

In all working Saudi gold mines, ores are treated using the hazardous cyanidation process. Some Saudi gold ores, such as Al-Amar, is known to be refractory to cyanidation. In this work, we have examined the extraction of gold from Al-Amar gold ore by the much environmentally safer and efficient thiosulfate process. The run of mine (ROM) and carbon-in-leach (CIL) feed, that is obtained after separation of copper concentrate from ROM, samples were found to contain 6.5 and 3.6 ppm gold, respectively. The mineralogical microscopic investigations of ROM samples confirmed that fine gold specks were scattered and encapsulated inside sulfide or quartz base minerals. This could explain the expected reason of the difficult leaching of gold by cyanidation. The X-ray diffraction analysis showed that the CIL feed contained quartz, pyrite, sphalerite and chlorite minerals. After detailed leaching studies of CIL feed, almost 70% of gold could be extracted at 0.2 M ammonium thiosulfate and 0.3 M ammonium hydroxide after 24 h. Addition of copper(II) as <0.2 mM only slightly enhanced the gold leaching in the ammoniacal thiosulfate solution. Gold leaching drastically decreased as the concentration of copper(II) increased 0.2 mM due to the degradation of S2O3²¯.

3

Enhanced solvent extraction of cadmium and iron from phosphoric acid in chloride media

Mahmoud M. H. H., Mohsen Q.

Physicochemical Problems of Mineral Processing

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2011

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Vol. 47

27-40

EN

Cadmium and iron are common impurities in wet process phosphoric acid (WPA). These impurities should be minimized to the acceptable levels before the commercialization of the WPA. Organic extractant such as trioctylammine (TOA) will be protonated in acidic media and can act as a liquid anion exchanger for separation of anionic chloro-species of Cd2+ and Fe3+ from WPA. Synthetic solutions containing phosphoric acid, 40 ppm Cd2+ and 3% Fe3+ (calculated as Fe2O3) were prepared and the different parameters affecting the extraction of these metal ions with TOA were investigated. The extraction of the two metal ions was found to be neglected in absence of chloride ions and it sharply increased by increasing HCl concentration. More than 98% of Cd2+ was extracted with 20% TOA in kerosene from 30% H3PO4 in presence of 1-3% HCl. Almost complete extraction of Fe3+ was achieved in presence of 10% HCl at similar experimental conditions. The TOA concentration of about 10% and 30% could completely extract Cd2+ and Fe3+ at 10% HCl for 10 min, respectively. A third phase formation was observed when TOA in kerosene was contacted with acidic aqueous solutions and this was eliminated by modification of TOA with 10% n-octanol but the extraction efficiency was slightly declined. The extraction process was quite fast, where 3 minutes was found to be sufficient for equilibrium extraction of both metal ions. Increasing the H3PO4 concentration enhanced the extraction of Fe3+ but little affected that of Cd2+. Most of the two metal ions can be easily stripped by contacting the loaded TOA with water but emulsion formation was observed and the phase separation was difficult. Acidic solutions such as 0.5 M HClO4 can solve the problem and strip about 90% of both metal ions. Small amount of H3PO4 (about 1% of the started acid) was co-extracted and stripped together with Cd2+ and Fe3+ under same conditions.