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This study assesses cyanide and cyanidation wastes management practices among small, medium and large-scale gold leaching plants in Siaya County, Kenya. The socio-economic benefits of gold extraction through cyanidation of mercury-contaminated tailings notwithstanding, the study establishes inadequate cyanide and cyanidation wastes management practices which could potentially cause significant environmental and human health impacts. Through structured key-informant interviews with operators from 15 selected gold leaching plants of varying scales of operation, along with field observations, and quantitative analysis utilizing both bivariate and inferential statistical tools, the study reveals inadequacies in cyanide, cyanidation wastewater, and tailings management practices. Key findings highlight widespread contravention of the international cyanide management standards and lack of adoption of advanced cyanidation wastes treatment technologies. Moreover, the study examines Political, Economic, Social, Technological, Environmental, and Legal factors as external factors affecting the management of cyanidation wastes. Consequently, the study recommends adoption of comprehensive cyanide management practices as outlined in the Cyanide Code and technological upgrades to mitigate potential environmental and human health impacts, and enhance regulatory compliance in gold cyanidation. In a nutshell, this study underscores the urgent need for stringent enforcement of environmental and mining industry laws and regulations in order to protect the environment and public health in gold mining regions. These measures are vitally important to ensure responsible mining practices and uphold environmental stewardship while promoting economic growth.

The paper presents the results of the research on the intensification of the cyanidation process of low sulphide gold bearing ore from the Burgunda deposit with relatively simple material composition. To intensify the process, it is proposed to conduct comparative research on three methods: direct cyanidation and cyanidation in the grinding cycle, including the supply of oxygenated recycled water. The results of the kinetic research showed high efficiency of the third method - cyanidation in the grinding cycle with supply of recycled water pre-saturated with oxygen up to the concentration of 15.8 ppm. It made it possible to achieve both high levels of gold recovery and transition of the gold dissolution rate to the kinetic range.

To clarify the development potential of Karan-type gold deposits, this study conducted systematic process mineralogy research on samples of this type. Using scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and automated detection analysis software (BPMA), the research revealed that the gold content in the samples was 2.52 g/t, primarily existing as native gold (91.43%) and argyrochondrite (8.57%). Gold minerals were embedded in particles smaller than 5 μm, predominantly as encapsulated gold (67.11%). The main harmful element, arsenic (0.40%), existed as arsenopyrite, while pyrite (the primary sulfide mineral) accounted for 10.13% of the ore. Results showed that under conventional full mud cyanidation conditions with 90% fine particles below 200 mesh, the leaching rate was only 32.14%, indicating extremely difficult-to-leach minerals. The embedded characteristics of gold minerals in this raw ore severely constrained cyanidation efficiency. Therefore, by clarifying the ore’s process mineralogy features and developing targeted pretreatment processes to improve gold mineral dissociation, the ultra-fine grinding-oxidation pretreatment-leaching process was ultimately selected. This approach effectively resolved the low leaching efficiency issue caused by sulfide-encapsulated gold minerals in complex gold deposits containing sulfides (pyrite, arsenopyrite). After thorough optimization of grinding fineness, dissolved oxygen, oxidation time, and the gold leaching rate increased significantly to 64.29%, demonstrating the effectiveness of this process for Karan-type gold ore leaching.

The most common method used for gold processing in artisanal and small-scale mining is amalgamation using mercury as a gold extracting agent. Indonesia is one of the countries that ratify the Minamata Convention, meaning that Indonesia has agreed to reduce or even eliminate the use of mercury. Some methods for replacing mercury as a gold-extracting agent are cyanidation and borax. The research aims to determine whether the miners in Pelangan still use mercury in gold processing. The method of this research is observation, interviews, and literature review. The data obtained were then analyzed descriptively. The result indicates that the miners in Pelangan Village use two methods of gold processing from ore: (1) amalgamation using mercury followed by cyanidation and (2) cyanidation. Most of the miners use the cyanidation method without going through amalgamation. The main reason they do not use mercury are amalgamation method yields low gold recovery and the price of mercury is high. This indirectly shows that the miners in Pelangan Village have contributed to efforts to reduce mercury use in Indonesia.

Copper precipitate comes from cyanidation wastewater treatment process using AVR (acidification-volatilization-regeneration) technology in a Korean gold plant and typically assays 44.53 wt % Cu, 5.56 wt % Fe and 16.81 wt % S. CuSCN and Cu 2 Fe(CN) 6 are major copper compounds in the precipitate and in the past it has been sold as raw material for pyrometallurgy of copper. Low-temperature ( ) sulfuric acid baking followed by acid leaching has been evaluated in order to recover copper and the experimental results showed that by acid baking under following condition: 250°C, 60 min and ratio of 98 wt % H 2 SO 4 /copper precipitate 2.4, ~98.5 wt % copper was released to the leach solution. During baking Cu 2 Fe(CN) 6 preferentially reacted with sulfuric acid over CuSCN. The leachate containing Cu and Fe can be sent to conventional SX-EW process to produce electrolytic copper. And a little residue (~3.2 wt % of copper precipitate weight) is formed after acid leaching, Cu content in it is 20.8 wt % and Cu 2 S and CuS are major copper compounds. Possible reactions were proposed for sulfuric acid baking of copper precipitate. HCN formed during baking is reoxidized to CO 2 and N 2 , so recovery of cyanide during baking is of no significance. Based on this investigation, new process for treatment of copper precipitate is proposed for copper recovery. The process mainly consists of acid baking, acid leaching and SX-EW. And treatment of off-gas is needed in view of environmental issue.

The global gold ore grade has been decreasing, and the mineralogy is now more diverse and complex. This has necessitated the utilization of low-grade ores previously not used. During the cyanidation process of such ores, copper cyanide complexes form that are competitively adsorbed with gold onto activated carbon. Therefore, to decrease the amount of copper in the pregnant electro winning electrolyte, a series of copper adsorption experiments were done to limit the amount of copper that adsorbs onto activated carbon. Tests on selective copper cold stripping were also conducted to selectively elute copper from loaded head carbon before the elution process. The results showed that increasing the solution pH from 9 to 11 decreased the copper adsorption from about 15.1% to 8.2%, but on the other hand the gold adsorption decreased from 98.7% to 95.1%. The optimal determined cold stripping parameters were 2% cyanide strength, 1% sodium hydroxide, 27 g/L carbon concentration and 4 h residence time. This experimental procedure effectively reduced the amount of copper in the gold leaching process and has potential to be used in large-scale applications.

The present work focuses mainly on the study of electrochemical phenomena induced by the presence of sulfide minerals during silver cyanidation. Firstly, an electrochemical study was carried out to characterize the electrochemical behavior of silver electrode in cyanide solution. The obtained results were useful to explain the mechanism of silver dissolution by cyanidation. Secondly, the effect of oxidants type and cyanide concentrations was carried out in order to identify optimal conditions for silver dissolution. Based on the obtained results, cyanidation tests were carried out in the absence and in the presence of sulfide minerals (chalcopyrite, sphalerite and galena). The results obtained by electrochemical methods (Open circuit potential, polarization curves, cyclic voltammetry, Tafel curves), complemented with scanning electron microscope (SEM) examination coupled with energy-dispersive X-ray spectroscopy (EDX), reveal that the limitation of silver cyanidation can be attributed to several factors. Passivation phenomenon occurs in the presence of galena, while galvanic interaction takes place in the presence of sphalerite. Chalcopyrite displays different impacts through liberated copper ions that overconsume available free cyanide. According to this study, impact of sulfide minerals on silver dissolution varies in the following order: chalcopyrite > galena > sphalerite.

The surface wettability of pyrite, as the main gold-bearing mineral in cyanide tailings, significantly influences flotation performance. This work discusses the interaction mechanism between CN and the pyrite surface using XPS and etching (via ToF-SIMS signals). Additionally, the contaminant species affecting the contact angle of the pyrite surface were determined. The results showed that CNO /SCN and FeCN /FeSCN were major and minor cyanide-containing substances on the surface of cyanide pyrite, respectively. After 24 h of cyanidation, a deposition film with a depth of 16.75 nm formed on the pyrite surface. Principal component analysis was employed to assist time-of-flight secondary ion mass spectrometry (ToF-SIMS) in further studying the distribution of contact angles of cyanide-pyrite particles. The results demonstrated that the variation of surface sessile drop contact angle values of pyrite was correlated with the chemical complexity. A ToF-SIMS contact angle model containing three secondary ion peaks of CN , SCN , and FeOOH+ was derived to predict the contact angle on the surface of cyanide pyrite and provide technical support for the secondary resource utilization of cyanide tailings.

It is known that the tailings of gold mines have brought serious heavy metal pollution; however, the heavy metal pollution caused by gold tailings in specific geological environments and extraction processes still must be studied. This study investigated the distribution, speciation, bioaccumulation, and pollution of heavy metals in soils from the Yueliangbao gold tailings area in central China, where gold was extracted by cyanidation. The results show that the concentrations of Cu, Pb, Zn, Mn, Mo, and Cd in the soils of the tailings pond were higher than those in the local background. The concentrations of heavy metals related to mineralization activities, such as Cu, Pb, Zn, and Mo, varied with the distance to the tailings pond center. There was a decreasing trend of tailings pond center > tailings pond entrance > surrounding environment. This study’s gold tailings pond differed from those of other regions because of its high content of unextracted Cu remaining in the pond. The proportion of non-residual Cu in the tailing pond soil was much higher than that of residual Cu, indicating it was likely to migrate to the surrounding environment. The pollution assessment indicated that the tailings pond soils were heavily polluted by Cu, and the level of heavy metal pollution in soils was positively correlated with the distance to the tailings pond center. Consequently, this tailings pond may become a source of Cu pollution in the surrounding environment, thus endangering environmental safety and human health. The study of heavy metal concentrations in the dominant plants showed that Chinese brake ( Pteris vittata L.), Ramose scouring rush ( Equisetum ramosissimum ), and Manyflower silvergrass ( Miscanthus floridulus ) had the potential to be used for the phytostabilization of Cu.

The gold recovery from cyanidation tailings was only 4.01% with the general flotation process, the surface analyses of flotation products were performed, and the results showed that the poor gold recovery with general flotation process was due to the passive films covering the surface of the gold bearing pyrite. These films are mainly hydrophilic hydroxides of Ca, Fe and Mg, at the same time, the depression of CN– to pyrite flotation in the flotation slurry was also a main contributing factor. With the surface repair regeneration procedures, it was proven that sulfuric acid pretreatment plays a dominant role in the removing and cleaning of passive films, while destroying free cyanides in the slurry. Sodium carbonate was then used as a buffering pH modifier and as a slurry dispersant after sulfuric acid pretreatment. The gold recovery was as high as 93.41%, compared to the original gold recovery of 4.01%.