Oktay Celep

Characterization of refractory behaviour of complex gold/silver ore by diagnostic leaching

The amenability of a refractory ore to the extraction of gold and silver by cyanide leaching was investigated. Diagnostic leaching tests were also performed to shed light on the refractory characteristics of ore. The leaching tests show that the extraction of gold and silver is consistently low, i.e. �047% and �019.2%, respectively, over a leaching period of 24 h. Even fine grinding (e.g. �y38 μm) does not improve the recovery of gold and silver. Diagnostic leaching approach provides information into the cause of the refractoriness of the ore. The findings suggest that the refractoriness is induced by the dissemination and encapsulation of the very fine gold and silver particles largely in the carbonates, oxides and sulfides and, to a small extent, with silicates present in the ore matrix. These findings highlight the practical importance of diagnostic leaching for the understanding of the refractory characteristic of such an ore and for the identification of possible pretreatment options to overcome its refractoriness prior to cyanide leaching.

Improvement of Silver Extraction by Ultrafine Grinding Prior to Cyanide Leaching of the Plant Tailings of a Refractory Silver Ore

Ultrafine grinding (UFG) was proposed as a pretreatment method prior to cyanide leaching of old plant tailings of a refractory silver ore. Direct cyanidation of the as-received tailings (d80: 100 µm) led to a low silver extraction of only ≤43% over 24 h. A size-based diagnostic study has demonstrated that the refractoriness of the tailings is essentially physical in character. Therefore, effects of particle size/UFG (d99: 5–75 µm), concentrations of NaCN (0.75–2.25 g/L) and Pb(NO3)2 (0–500 g/t) on the extraction of silver were investigated using a Box–Behnken design. The statistical analysis of the experimental data (%Ag extraction at 1 h) revealed that particle size/UFG was the most significant parameter for the extraction of silver, which was substantially improved after UFG. A positive effect of increasing the concentration of NaCN was also observed particularly at finer particle sizes while the effect of concentration of Pb(NO3)2 was insignificant. Almost complete extraction for silver (i.e., ≥99%) was demonstrated to be possible at even higher concentrations of cyanide (>2.25 g/L NaCN) when using the finest material (d99: 5 µm) over only 1 h of leaching. Albeit, the consumption of cyanide tended to increase with UFG or increasing the initial concentration of cyanide. The findings showed that UFG can be used as a suitable and environmentally sound pretreatment method to improve the extraction of silver from the refractory silver ore tailings. The diagnostic approach adopted in the current study has proved to be a useful analytical tool to determine the amenability of the ore to ultrafine-grinding as a pretreatment process.

Characterization of an iron oxy/hydroxide (gossan type) bearing refractory gold and silver ore by diagnostic leaching

Abstract A detailed characterization of an iron oxy/hydroxide (gossan type) bearing refractory gold/silver ore was performed with a new diagnostic approach for the development of a pretreatment process prior to cyanide leaching. Gold was observed to be present as native and electrum (6–24 µm in size) and associated with limonite, goethite and lepidocrocite within calcite and quartz matrix. Mineral liberation analysis (MLA) showed that electrum is found as free grains and in association with beudantite, limonite/goethite and quartz. Silver was mainly present as acanthite (Ag 2 S) and electrum and as inclusions within beudantite phase in the ore. The cyanide leaching tests showed that the extractions of gold and silver from the ore ( d 80 : 50 µm) were limited to 76% and 23%, respectively, over a leaching period of 24 h. Diagnostic leaching tests coupled with the detailed mineralogical analysis of the ore suggest that the refractory gold and silver are mainly associated within iron oxide mineral phases such as limonite/goethite and jarosite-beudantite, which can be decomposed in alkaline solutions. Based on these characterizations, alkaline pretreatment of ore in potassium hydroxide solution was performed prior to cyanidation, which improved significantly the extraction of silver and gold up to 87% Ag and 90% Au. These findings suggest that alkaline leaching can be used as a new diagnostic approach to characterize the refractoriness of iron oxy/hydroxide bearing gold/silver ore and as a pretreatment method to overcome the refractoriness.

Ultra fine grinding of silver plant tailings of refractory ore using vertical stirred media mill

Abstract Ultra fine grinding of the plant tailings of a refractory silver ore was studied using a laboratory type vertical stirred media mill. Preliminary tests confirmed that ultra fine grinding substantially improves the extraction of silver from the tailings in cyanide leaching (i.e. 36% Ag extraction rate from the as-received tailings with d80 of 100 μm, c.f. 84% extraction rate after ultra fine grinding of the tailings with d80 of 1.2 μm). In the ultra fine grinding tests, the effects of ball diameter (2–4.5 mm), stirring speed (200–800 r/min) and ball charge ratio (50%–80%) on the fineness of grind (d80, μm) were investigated through a Box–Behnken design. Increasing stirrer speed and ball charge ratio decreased fineness of grind while larger balls resulted in the coarser products. The tests demonstrated that a fineness of grind less than 5 μm can be achieved under suitable conditions. Analysis of stress intensity indicated an optimum range of stress intensity of (0.8–2)×10−3 N·m for all power inputs.

Diamond recovery from waste sawblades: A preliminary investigation

Due to their excellent hardness and toughness, diamond tools have been widely used as cutting tools for mining applications such as machining and/or processing of natural stones. A considerable amount of used sawblades with diamond grits are damaged, scrapped and wasted in the regions where machining and/or processing of ornamental stones are heavily conducted. Since a damaged and/or scrapped sawblade could still have diamonds grits, the recovery of diamond grits from sawblades has recently gained attention. The aim of this study was to investigate the recoverability of diamonds from damaged sawblades using hydrometallurgical processes, including aqua regia. Using scanning electron microscopy micrographs, the worn surfaces of diamonds were also examined before and after leaching. The results of the study represented that the diamonds from damaged sawblades can be successfully recovered by hydrometallurgical processes, including aqua regia, and the recovered diamonds could be reused in cutting tools after size classification. The results also revealed that among the damage types of diamond, the fractured and polished crystals resulted in diamond crystals with lower grain size.

Removal of Cyanide from Solutions by Air Oxidation and Adsorption

In this study the removal of free cyanide from aqueous solutions by air oxidation and adsorption was investigated. Effects of air and pure oxygen, and catalyst on the rate and extent of the removal of cyanide were studied. It was found that the oxidative removal of cyanide by air/oxygen was very limited although it tended to improve in the presence of pure oxygen and catalyst such as activated carbon and copper sulphate. In the presence of continuous aeration, the non-oxidative removal of cyanide was correlated with a decrease in pH effected apparently by the transfer of carbon dioxide from air phase into the medium. The removal of cyanide by adsorption on activated carbon (AC), nut shell (NS) and rice husk (RH) was also examined. Adsorption capacity of activated carbon was shown to be significantly enhanced via impregnation of activated carbons with metals such as copper (AC-Cu) and silver (AC-Ag). In the column tests, the breakthrough capacity of adsorbents was found to be in an increasing order of RH