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Cyanidation is the most widely used technique for gold extraction worldwide. However, its efficiency in gold extraction has decreased due to gold association with base metals such as copper. Copper is known to form different complexes with cyanide depending on the pulp pH. These Cu-CN complexes deplete the pulp of free cyanide, thereby decreasing gold leaching. The study examined the application of diethylenetriamine (DETA) in cyanidation to minimise copper ions effect on gold cyanidation. Leaching tests performed in the presence of copper ions reduced gold recovery from 93% to 15% at a copper sulphate concentration of 1% and increased cyanide consumption by 10%. The introduction of DETA (between 0.2% and 1%) however restored gold recovery back to normal as the baseline without copper ions and also enabled gold extraction at a reduced cyanide strength. Based on the study, DETA could be used during gold–copper cyanide leaching to minimise the copper ion effect and enhance gold extraction. [ABSTRACT FROM AUTHOR] more...

Gravity gold characterization provides a comprehensive understanding on the effect of mineralogy, particle size, and liberation on gravity concentrator performance. This is of significant economic importance for gold ores with a high amount of coarse gold particles. In this study, the effect of pulp rheology on gravity recoverable gold (GRG) was investigated using a single-stage GRG test on paleoplacer gold deposits of the Tarkwaian system of Ghana. The elemental and mineralogical composition of the gold ore was characterized using ICP-MS, XRD, and QEMSCAN analyses. Bench-scale gravity concentration was performed on the gold ore at varying clay contents (in the range of 5–30 wt.%) using Lab Knelson concentrator in the absence and presence of NaOH (2.5 kg/t) and CaO (2.5 kg/t). The mineralogical analysis showed the ore is oxidized and comprised 88% Quartz, 8% muscovite mica, 2% hematite, and 2% kaolinite. Liberation and association analyses showed 58% of the gold particles were liberated, 1% formed binary with quartz, and 41% formed complex aggregates with other mineral phases. The gravity concentration of the ore without clay material yielded 51% Au recovery (11.2 g/t) at the grind size of 80% passing 106 µm. Partial replacement of the ore with clay material at 5%, 10%, 15%, 20%, and 30% decreased gold recovery from 51% to 25.7%, 12.7%, 8.8%, 5.1%, and 1.5%, respectively. Subsequent conditioning of the slurry with NaOH improved gold recovery due to possible improvement in slurry rheology. However, the addition of CaO decreased gold recovery due to an increase in slurry viscosity. [ABSTRACT FROM AUTHOR] more...

The present study investigates the effect of aeration and diethylenetriamine (DETA) on the selective depression of pyrite in a porphyry copper–gold ore, after regrinding (at grind sizes, d 80 = 38 and 8 μm) with respect to Au recovery and grade using oxygen demand tests, flotation, QEMSCAN, X-ray spectroscopy (XPS) and EDTA extraction analysis. It was found that pyrite depression increases after aeration and with decreasing grind size. This was observed to be due to the markedly higher oxygen consumption rate of pyrite at the 8 μm (kla = 0.10 min −1 ) than at the 38 μm grind size (kla = 0.02 min −1 ). The addition of DETA improved pyrite depression (9% with aeration only versus 39% with aeration + DETA) at the 38 μm grind size. Gold and copper flotation recovery followed pyrite recovery for the two grind sizes using XD5002 in the presence of air and DETA. The surface analysis (XPS and EDTA extraction) revealed that the significant pyrite depression at the 8 μm grind size was due to increased amount of surface iron oxides, oxy-hydroxides (Fe O/OH), sulphate species and increased liberation of mineral phases (QEMSCAN analysis), whilst the poorer pyrite depression at the 38 μm grind size was due to insufficient liberation of mineral phases and the persistence of activating Cu on the pyrite surface. The addition of DETA increased pyrite depression at the coarser grind size due to a significant reduction in Cu(I)S and increased Cu(II) O species, correlating with the flotation results of pyrite under this test condition. Two-stage copper and pyrite flotation, followed by Au cleaning after regrinding to 38 μm grind size, under high pH or aerated condition is proposed as the recommended route to optimise Au flotation. [ABSTRACT FROM AUTHOR] more...

The present study investigates the implications of gold mineralogy on its flotation recovery, in a typical porphyry copper–gold ore (1.7g/t Au feed grade). Also, flotation strategies to optimise gold recovery and grade without compromising copper recovery and grade were examined. The approach used in this study involves a combination of different mineralogical techniques such as quantitative X-ray diffraction (QXRD) and scanning electron microscopy (QEMSCAN). Based on the mineralogical information obtained, different collector regimes involving sodium iso-butyl xanthate (SIBX), N-butoxycarbonyl-n butyl thionocarbamate (XD5002), mercaptobenzothiazole (MBT) and dithiophosphate (DTP) at different grind sizes (p80, i.e. a nominal product size of 80wt% passing (a) 70µm and (b) 38µm screen) were tested to examine the flotation behaviour of gold in relation to copper recovery. Chalcopyrite and covellite are the principal copper mineral phases in the ore, with pyrite as the main sulphide gangue mineral. Quartz, Fe oxide and carbonates were identified as the main non-sulfide gangue minerals. The identified gold particles occurred as either liberated particles (∼10–22µm) or fine inclusions (∼1–3µm) in pyrite, biotite and sphalerite. Two-stage flotation (copper and pyrite rougher stages) at a p80 of 70µm indicated that high gold (95.2%) and copper (97.4%) recovery can be achieved, but the levels of pyrite in the concentrate are also very high (49.1%). At finer grind (p80=38µm) and without pyrite flotation stage, gold recovery decreased from 95.2% to 73%, but at an improved grade (5.3g/t) compared to 3.5g/t in the baseline. This approach improved gold grade significantly due to a drastic reduction in pyrite recovery. The flotation study indicates that the collector regime, SIBX/XD5002 (at 38µm feed size) gives the maximum gold recovery and grade while rejecting significant pyrite without compromising copper recovery and grade. Further studies are warranted to identify means of recovering Au from the copper flotation tail. [ABSTRACT FROM AUTHOR] more...

Abstract: There is a considerable challenge in accurate characterisation of gold (Au) particles in low-grade plant ore mineral samples. This is particularly true for automated mineralogical tools such as X-ray micro-computed tomography (Micro-CT) and scanning electron microscopy (SEM), where the need for statistically meaningful numbers of particles requires many sections to be analysed. Whiles the Vertical Gas Stream (VGS) elutriator is suitable for coarse particle upgrading (i.e. >38μm), the performance is poor for finer particles (i.e. <38μm). Consequently, the system has been modified to Vertical Water Stream (VWS) elutriator using higher density fluid (i.e. water) to enable analysis of Au particles below 38μm. In this work, the VGS system was used to upgrade Au particles in the −53+38μm size fraction (in rougher concentrate, rougher tailings, regrind mill discharge and regrind cyclone underflow) and the VWS system was used to upgrade Au particles in the −38μm size fraction of the regrind mill discharge sample. The VWS elutriator was calibrated using galena (specific gravity, S.G. of 7.58) and quartz (S.G. of 2.65) particles of <38μm size as model minerals. From the calibration tests, partition curves as a function of particle size were generated. Using these measurements, theoretical partition curves for Au (S.G. of 19.3) have been calculated. The VWS concentrate was characterised using Micro-CT and compared with SEM coupled with energy dispersive X-ray (EDX) analysis of −53+38μm ore size fraction of the VGS concentrate of the four sample streams. The Micro-CT analysis of VWS Au concentrate showed that sufficient particles (Au) can be upgraded. SEM/EDX results indicate that regrind does not affect changes in free Au particle morphology, aspect ratio and frequency of shearing damage in the −53+38μm size fraction. Cyclone classification of the regrind mill discharge in the −53+38μm size fraction appears to perform surface cleaning by exposing obscuring silver (Ag) surfaces on Au particles in the mill discharge sample. [Copyright &y& Elsevier] more...