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Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium, and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. This work presents a thermodynamic analysis of a monazite system and discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extractions and low acid consumption. Rare earth extractions as high as 80% were achieved, while iron and thorium extractions were lower than 1%, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature.

This paper describes a detailed chemical characterization of connector pins separated from diverse electronic components removed from waste printed circuit boards (WPCB) of computers. Chemical maps by SEM-EDS (Scanning Electron Microscopy - Energy Dispersive Spectroscopy) indicated that the substrates of all connector pins are made by Cu-Sn, Cu-Zn or Cu-Sn-Zn alloys, which are covered by thin Ni and Au layers. The ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) analysis of the different connector pins revealed that these materials are mostly constituted by Cu (62–88% w/w) and very attractive Au contents were found (up to 1273 g/t). For all pins, intermediate contents of Zn, low contents of Ni, Sn and Pb and very low contents of Pd and Fe were determined. A heterogeneous, 100% metallic sample was prepared by mixing all individual connector pins aiming at contribute to the development of feasible technologies for recovering valuable metals. The mixed sample contains about 73% w/w Cu and 168 g/t Au, which are higher than the contents reported in the literature for samples obtained after grinding assembled or disassembled WPCB. The leaching of the mixed sample without grinding and concentration steps will reduce operating costs and maximize metals recovery avoiding mass losses.

This paper describes the effect of zinc ions on copper speciation and adsorption on activated carbon in solutions with varied cyanide levels and containing calcium. Batch and column adsorption experiments were carried out under atmospheric conditions at different levels of CN/Cu using two types of activated carbon. Raman analysis shows that CN/Cu molar ratio, ionic strength (by adding calcium ions to the solution), and zinc ions can be used to control copper speciation in cyanide solutions. The addition of Zn2 + to cyanide solutions causes the conversion of CN− and Cu(CN)43 − species to Cu(CN)32 −, and the concomitant formation of Zn(CN)42 −, regardless of cyanide concentration and ionic strength. As Cu(CN)32 − has a high affinity for the solid surface, copper adsorption was favored. The co-addition of Ca2 + to the solutions produces an even larger enhancement of copper adsorption on activated carbon and has no effect on zinc adsorption. Column experiments show a significant reduction in the volume of cyanide solution to be further treated and an important increase in the concentration of copper. These findings may aid in the design of copper and cyanide recovery strategies.

The current paper describes the effect of key operating variables (i.e. pH, presence of sodium sulfate, boric acid and sodium lauryl sulfate – SLS) on important features of nickel deposits by means of morphologic and surface roughness analyses and indentation hardness tests. Two substrates (cathodes) were used: 316 L stainless steel (SS) or titanium (grade 2). Only changes of pH and additions of Na2SO4 and SLS to the electrolyte largely affected the morphology of the deposits, regardless of substrate type. At pH 3, a condition in which relatively high values of current efficiencies were obtained, the addition of 155.9 g L− 1 of Na2SO4 or 10 mg L− 1 of SLS to the electrolyte lead to the production of Ni deposits with few hydrogen pits on the surface and regular edges. However, the presence of 155.9 g L− 1 of Na2SO4 in the electrolyte caused an increase of the average roughness of the deposits in the order of 27 and 54% when 316 L SS or Ti cathodes were used, respectively. By adding 10 mg L− 1 of SLS to electrolyte containing 155.9 g·L− 1 of Na2SO4 and 8 g L− 1 of H3BO3, the surface roughness decreased about 24 and 17% when 316 L SS or Ti cathodes were used, respectively, without any effect on the materials' microhardness. The results of this work suggest that only the replacement of 316 L SS blank cathodes by Ti may not represent significant benefits in terms of product quality.

This work describes the stripping behavior of zinc cathodes with focus on the effect of current density, fluoride ion concentration in the electrolyte and acidity on their adherence to the aluminum blanks. The adhesion strength was measured using a customized stripping device that reproduces the loading submitted to the deposit in the conventional stripping operations. The force versus displacement plots exhibited a similar behavior: initial increase of the force to a peak value, followed by its gradual decline to a nearly stable value, and by a final increase until the required value to detach the deposit is reached. This increase registered at the final stage was associated with the relatively higher thickness of the metal deposit. Around the corners of the aluminum plate, which represent sites with a relatively higher charge density, the product exhibits a higher thickness and crystallites with a smaller grain size. The adhesion strength was estimated from the force registered at the intermediate stage, which comprises (i) the component required to bend the sample, (ii) the component related to the adhesion between the deposit and the aluminum plate and (iii) the component associated with the friction between the deposit and the steel blade of the stripping device. The measurements revealed an increase of the adhesion strength and energy required for stripping by increasing the current density and fluoride ion concentration, but the effect of acidity on both the parameters was found to be negligible. The effects of fluoride ion and current density were related to the observed decreases in the average sizes of the first grains of the zinc deposits due to high nucleation rates.

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS2) in gold mining tailings. This work examined the galvanic effect of FeS2 on As release from FeAsS oxidation in circumneutral media under oxygen-depleted and oxygen-saturated conditions. The oxidation experiments were conducted with a flow-through reactor in the absence of FeS2 particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS2 particles causes an increase in the accumulated As release, mainly under O2-saturated conditions. At 30% wt. FeS2, the increases relatively to FeS2-free conditions were 82% and 117% in O2-depleted and O2-saturated solutions, respectively. At steady-state, the As release rates increased from (4.9 ± 0.5)× 10−4 µmol m−2 s−1 (0% wt. FeS2) to (1.1–1.9)× 10−3 µmol m−2 s−1 (5–30% wt. FeS2) under O2-saturated conditions. Analysis of FeAsS samples after oxidation revealed oxidized particles partially or entirely covered by precipitates with different sizes, shapes and compositions (e.g., As−S−bearing ferrihydrite, elemental sulfur, and As−O phases). A fine (3–4 nm thick) amorphous layer of S−As−bearing ferric oxy-hydroxide was also identified on oxidized FeAsS, with Fe(III) and As(III) species.

The present work describes the effects of certain organic compounds used in industrial operations on nickel electrowinning and product quality. The organic compounds tested here consisted of a commercial extractant (Cyanex 272), a diluent (Escaid 110), a flocculant (Flonex 910), a lubricating oil (Lubrax Hydra 68), and an acid mist suppressant (Fluorad FC-1100). The electrowinning experiments were conducted under operating conditions (i.e. nickel concentration, pH, temperature, and current density) commonly applied in industries. The results indicated that the extractant, the diluent, and the lubricating oil do not affect the current efficiency (CE) or cell voltage (CV) at levels 0–100 mg L− 1, while the flocculant and acid mist suppressant caused negative impacts on the electrowinning process. The CE dropped from 93.6% (organic-free electrolyte) to 86.0% and 92.8% in electrolytes containing 100 mg L− 1 of acid mist suppressant and flocculant, respectively. Measurements by cyclic voltammetry showed that Ni2 + reduction starts at more negative potentials in the presence of the flocculant and the acid mist suppressant, thereby indicating an inhibition of the deposition reaction. Regarding the deposit quality, all organic compounds (except diluent) increased hydrogen pitting at 100 mg L− 1. The addition of the acid mist suppressant showed the most negative impact, resulting in the delamination of the Ni deposit at 50 and 100 mg L− 1, likely due to a decrease in the crystallite size. Metallographic analysis indicated that the type of deposit microstructure was modified when the electrolyte contained the flocculant and acid mist suppressant. As regards the effect on the Ni deposit's nanohardness, the measurements indicated that the flocculant and the acid mist suppressant, at 100 mg L− 1, strongly increased nanohardness by approximately 31% and 72%, respectively. This increase in nanohardness consequently decreased the material's ductility, which may affect the stripping and cutting of the Ni sheets.

The selective cementation of cadmium, cobalt, and nickel from synthetic and an industrial zinc sulfate (150–160 g.L−1) electrolyte was investigated. The desired cadmium removal (from 640 to 740 mg.L−1 to

This work evaluates the use of customized hybrid renewable energy system (HRES) with organic photovoltaic (OPV) cells for producing a high-purity metal by electrowinning. This process usually represents the most energy intensive step in the mining industry. A key advantage about the developed system is that the electric charge is inherently generated as direct current (DC), which can be directly supplied to the electrowinning cells without using intermediate rectifiers. This approach eliminates the energy losses associated, thus increasing the overall efficiency of the power system, and decreases the carbon footprint of the industrial facility. In this context, the main purpose of this first work was to evaluate the energy saving performance of the technology and its application to produce a quality product, which was characterized by morphology, crystal structure and bending behavior. The electrowinning of zinc was selected as case study. Thus, zinc electrodeposition tests were conducted under conditions practiced in industrial operations. The results demonstrated the proper functioning of the HRES system, since constant DC current was supplied to the process. The zinc cathodes exhibited morphology and structure typically described in the literature, which were ductile enough to allow bending without fracturing. On days with global horizontal irradiances in the range from 100 W m−2 to 1200 W m−2, 26 ± 4% of the total current supplied to the electrowinning cell was generated by the OPV cells used in this work. In Brazil, this performance corresponds to carbon mitigation of about 6.4 × 10−2 tons of carbon dioxide equivalents (CO2 eq) per ton of zinc produced. These findings indicate that hybrid systems with photovoltaic cells represent an alternative to save energy and increase the sustainability of electrowinning processes.

This paper evaluates the effect of zinc ions on copper electrodeposition. Although zincis not found at significant concentrations in conventional industrial copper electrolytes, in copper-concentrated sulfate leach liquors produced in the treatment of waste printed circuit boards (WPCB) its concentration may reach high levels. In this context, the effect of zinc on physical-chemical properties of copper sulfate electrolyte, performance indicators of copper electrowinning, and morphology and crystal structure of copper deposits were investigated. Copper electrowinning tests indicated that the current efficiency was negligibly affected by adding zinc (up to 75 g L−1) to synthetic copper sulfate electrolyte (30 g L−1 Cu2+ and 110 g L−1 H2SO4) at two levels of current density (250 A m−2 and 450 A m−2) and fixed temperature (35 °C). The energy consumption slightly increased: up to 4% at 250 A m−2 and up to 3% at 450 A m−2, both effects at 75 g L−1 Zn2+. This behavior was ascribed to decreases in the electrical conductivity of the electrolyte by adding zinc (up to 35% at 75 g L−1) and consequent increases in the ohmic drop and cell voltage. Electrochemical measurements by cyclic voltammetry and linear sweep voltammetry (LSV) indicated no cathode polarization by adding this impurity to the electrolyte, even at the highest level. In turn, the addition of zinc caused significant drops in the limiting current for copper deposition (e.g., the values recorded at 100 min−1 decreased about 60% when 75 g L−1 Zn2+ was added to the electrolyte). This effect was explained by the measured increases of electrolyte viscosity and calculated decreases of copper diffusion coefficient. The addition of 75 g L−1 Zn2+ to the electrolyte increased its viscosity in the order of 76%, and decreased the diffusion coefficient in the order of 45%. Regarding the effect of zinc on product quality, SEM analysis revealed negative effects on the morphology of the deposits (i.e., higher roughness and nodulation), mainly at the highest concentration of zinc and highest current density. XRD analysis showed modifications in the growth pattern of copper crystals under some conditions. For example, the addition of 30–75 g L−1 Zn2+ to the electrolyte led to the formation of (220) textured deposits at 250 A m−2. The findings of this work may be helpful to define proper operating conditions for copper electrowinning in order to produce high quality products, thus maximizing the recycling of copper from the selected secondary source.

BACKGROUND: Trauma is a leading cause of death and represents a major problem in developing countries where access to good quality emergency care is limited. Medecins Sans Frontieres delivered a standard package of care in two trauma emergency departments (EDs) in different violence settings: Kunduz, Afghanistan, and Tabarre, Haiti. This study aims to assess whether this standard package resulted in similar performance in these very different contexts. METHODS: A cross-sectional study using routine programme data, comparing patient characteristics and outcomes in two EDs over the course of 2014. RESULTS: 31 158 patients presented to the EDs: 22 076 in Kunduz and 9082 in Tabarre. Patient characteristics, such as delay in presentation (29.6% over 24 h in Kunduz, compared to 8.4% in Tabarre), triage score, and morbidity pattern differed significantly between settings. Nevertheless, both EDs showed an excellent performance, demonstrating low proportions of mortality (0.1% for both settings) and left without being seen (1.3% for both settings), and acceptable triage performance. Physicians' maximum working capacity was exceeded in both centres, and mainly during rush hours. CONCLUSIONS: This study supports for the first time the plausibility of using the same ED package in different settings. Mapping of patient attendance is essential for planning of human resources needs.© The Author 2016. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. Language: en

This paper evaluates the recovery of gold through selective acid leaching of connector pins removed from waste central processing units (WCPU) of computers. The exclusive treatment of this electronic component appears as a promising alternative since it minimizes gold losses. The experimental approach consisted by leaching steps of different types of pins aiming at dissolving all the metals that make up them, except the precious one. Analysis of the pins (2–6 mm length and ~ 1 mm diameter) by scanning electron microscopy coupled to energy dispersive spectrometry indicated (i) substrates made by copper, iron‑nickel alloy or iron‑nickel‑cobalt alloy; (ii) thin external gold coating; and (iii) thin nickel or nickel‑cobalt sub-coatings. Chemical analysis by inductively coupled plasma optical emission spectrometry revealed that the prepared sample consists mainly by copper (43 wt%), iron (26 wt%) and nickel (20 wt%); attractive contents of cobalt (4.6 wt%) and gold (1.4 wt%) were also determined. Due to the complex geometry of the pins and distinct reactivity of the different alloys, leaching stages were conducted in H2SO4-H2O2 media (1st step), HCl-H2O2 media (2nd step) and HCl media (3rd step). Under promising leaching conditions at 25 °C, all the metals were dissolved and then fine particles and thin foils of high purity gold (~99%) were recovered. Gold losses around 2–4 wt% were observed, mainly as result of its oxidation in the HCl-H2O2 media. The approach used in this work for treating the secondary source allowed the recovery of the precious metal with minimal losses, and it has potential to recover other valuable metals from the leach liquors.

The stability of Rare Earth Elements (REE), both sulfates and phosphates, was investigated using monazite ore, a residue from a synthetic rutile manufacturing process and a high-grade lanthanum sulfate sample. It was demonstrated that REE sulfates are converted into phosphates at temperatures within the range of 450–800 °C. This reaction depends on excess phosphorus present in compounds that are less stable than monazite. The presence of high partial pressures of P2O5 in the system will reconvert REE sulfates into insoluble REE polyphosphates – REE(PO3)3. Relatively high partial pressure may be attained by the decomposition of phosphorus compounds present in the sample, such as monocalcium phosphates and phosphoric acid generated by the addition of sulfuric acid. The direct contact with phosphoric acid leads, in turn, to the formation of monazite-like compounds. The gas–solid mechanism is believed to be the most suitable due to the easier access of the gas phase to the REE sulfate particles, thus making it possible to achieve the drastic decrease (conversion into phosphate) in REE extraction observed at 800 °C. This study’s results are expected to contribute to a better understanding of the factors favoring selectivity in REE extraction over iron from monazite ores.

Rare Earth Elements (REE) are fundamental for modern life products and green technologies. Supply constraints and the price peak of 2011 boosted intensive research for alternatives for processing and separation. Complex monazite-type, rare earth ores usually contain high acid consumption impurities, such as iron and aluminum, and radioactive thorium in their composition. These impurities are not removed by conventional concentration processes due to fine, micro-level association between the REE carrying minerals and the gangue minerals. This work presents a selective process route for REE extraction from iron-rich, monazite ores. The process involves sulfation by addition of concentrated sulfuric acid and pyrohydrolysis at temperatures of approximately 700–750 °C. Experimental results show REE extraction higher than 70% and low iron (below 5%) and thorium extraction (below 10%). A method based on thermogravimetric analyses was shown to be adequate to predict the behavior of a given ore sample in the sulfation-selective pyrolysis-leaching process.

This paper describes an experimental approach to evaluate the effect of organic impurities or even additives on metal electrowinning and product quality. In addition to electrowinning tests and electrochemical measurements, the approach includes organic analysis by Fourier Transform Infrared spectroscopy and gas chromatography; video monitoring of the reaction interface; and product characterization by using scanning electron microscopy, crystallographic texture and bending tests. The mechanical behavior of metal cathodes was assessed with a customized bending device that is able to bend the cathodes up to angles similar to that of the stripping machine. In this work, the effect of a potential organic impurity, lubricating oil, on the production of electrolytic zinc is taken as a case study. The findings of the investigation allowed a better understanding on the role of this organic on energy consumption and product quality and a qualitative prediction for the behavior of Zn cathodes during the stripping operation. Simple control and optimization procedures resulted in significant energy savings.

The role of organic reagents (flocculant and flotation collectors) and impurity (lubricating oil) in zinc deposition and in product quality is described in this paper. In the presence of a flotation collector for zinc and a lubricating oil, characterized by polar amine and non-polar alkyl groups, respectively, by using Fourier transform infrared spectroscopy, an inhibition of the metal nucleation process was observed, which was found to be particularly signi ficant for electrolyte contaminated with the amine-containing compound. The current ef ficiency (CE) dropped from 93.7% (organic-free solution) to 21.6% in the presence of 50 mg•L-1 of collector for zinc, and a negative but smaller effect was observed in the presence of similar amounts of the lubricating oil (90.7%). The addition of a flocculant and a collector for impurities, which contain the polar amide and carboxyl groups in their molecules, respectively, caused minor increases in the nucleation overpotential for zinc deposition and only at relatively high concentrations (100 mg•L-1). The addition of these compounds to the solution slightly increased CE. The characterization of the Zn deposits by X-ray diffraction and scanning electron microscopy revealed the formation of pores in deposits obtained from solutions containing the collector for impurities or lubricating oil, and different growth patterns were identi fied when the flocculant or collector for zinc was added to the solution. The observed trends have been interpreted in terms of the polar character and reactivity of the organic molecules to Zn2+ ion, and adsorption on the cathode surface.

This work describes the effect of some organic impurities on the quality of zinc deposits and on the efficiency of the electrowinning process. The presence of some organics (i.e., flotation collectors, flocculant and lubricating oil) in the sulfate electrolyte was shown to significantly decrease current efficiency, thereby increasing energy consumption. Microscopic and texture analyses revealed that the individual addition of these organics to the electrolyte leads to the formation of pores on the deposits, variations in their grain size, and orientation changes resulting in crystallographic randomization with a trend to reorient the crystals from a “perpendicular to the plane” to an “in plane” random distribution. The Zn electrodeposit's features are expected to affect mechanical properties and, in turn, the effectiveness of the stripping operation. Fil: Majuste, D.. Universidade Federal de Minas Gerais; Brasil. National Institute of Science and Technology on Mineral Resources, Water and Biodiversity; Brasil Fil: Bubani, F. C.. Universidade Federal de Minas Gerais; Brasil Fil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Martins, E. L. C.. Votorantim Metais - Zinc; Brasil Fil: Cetlin, P. R.. Universidade Federal de Minas Gerais; Brasil Fil: Ciminelli, V. S. T.. Universidade Federal de Minas Gerais; Brasil. National Institute of Science and Technology on Mineral Resources, Water and Biodiversity; Brasil

The interaction of anode and electrolyte chemistry in copper electrorefining is complex. This is especially true with regard to the behavior of Group 15 elements (As, Sb, and Bi). To better understand this system, laboratory electrorefining experiments were conducted using commercial anodes with As/(Sb + Bi) molar ratios of 0.54 and 3.8 and an electrolyte collected from a commercial refinery. The effect of adding thiourea during plating was also examined. Twenty-one hour copper deposits were produced in the laboratory to simulate starter sheet production. The mechanical properties of the electrodeposited copper as measured by an industrially relevant empirical bend test and a one-point bend test developed by UFMG are reported. The crystal structures of the samples were also examined.

Copper cyanocomplexes have been recognized as competitors for the adsorption sites of activated carbon during gold adsorption. In this paper, the effects of practical parameters (excess free cyanide, calcium ions and aeration conditions) on the selective adsorption of Au over Cu cyanocomplexes on activated carbon samples from different sources are discussed. In addition to the adsorption experiments, the aqueous and solid phases were characterized by Raman spectroscopy in an attempt to elucidate the observed trends. Four solid samples with different structures as regards the relative amount of graphitic planes and density of surface functional groups were selected. The results indicated the highest adsorption of Au and the lowest adsorption of Cu on the sample with the lowest density of surface groups and relative higher crystalline character. In contrast, the highest adsorption of Cu and the lowest adsorption of Au were obtained using the sample with the highest density of surface groups and relative lower crystalline character. These findings support the industrial application of activated carbons with low density of surface functional groups for gold recovery, such as the product obtained from coconut shell, and are consistent with the hypothesis of different preferential sites for the adsorption of Au and Cu. The results also indicate that if there is an excess of free cyanide in the solution, a higher Au/Cu selectivity is observed, but the Au loading on the activated carbon samples declines. In the presence of Ca2 + ions in the cyanide solution, positive effects on Au adsorption and negative effects on Cu adsorption were demonstrated for a CN/Cu molar ratio above 4 (i.e., Cu(CN)43 − as the predominant species), and these behaviors resulted in a higher Au/Cu selectivity. A previous adsorption of Ca2 + ions on the activated carbon surface creates new sites for Au(CN)2− adsorption, in addition to the graphene layers. From aerated solutions, the adsorption experiments revealed a positive effect on Cu adsorption, and negative impact on Au adsorption, thus affecting the Au/Cu selectivity. The aeration of the solution results in a decrease of the cyanide concentration, which reduces the CN/Cu molar ratio. Therefore, the addition of Ca2 + ions in the process solution and an optimal concentration of free cyanide, which should take into account the loss of cyanide by oxidation and volatilization, may help to improve Au/Cu selectivity.

Purpose While the orthopaedic management of open fractures has been well-documented in developed settings, limited evidence exists on the surgical outcomes of open fractures in terms of limb salvage in low- and middle-income countries. We therefore reviewed the Médecins Sans Frontières-Operational Centre Brussels (MSF-OCB) orthopaedic surgical activities in the aftermath of the 2010 Haiti earthquake and in three non-emergency projects to assess the limb salvage rates in humanitarian contexts in relation to surgical staff skills. Methods This was a descriptive retrospective cohort study conducted in the MSF-OCB surgical programmes in the Democratic Republic of Congo (DRC), Afghanistan, and Haiti. Routine programme data on surgical procedures were aggregated and analysed through summary statistics. Results In the emergency post-earthquake response in Haiti, 81 % of open fracture cases were treated by amputation. In a non-emergency project in a conflict setting in DRC, relying on non-specialist surgeons receiving on-site supervision and training by experienced orthopaedic surgeons, amputation rates among open fractures decreased by 100 to 21 % over seven years of operations. In two trauma centres in Afghanistan (national surgical staff supported from the outset by expatriate orthopaedic surgeons) and Haiti (national musculoskeletal surgeons trained in external fixation), amputation rates among long bone open fracture cases were stable at 20 % and

Copper cyanocomplexes have been recognized as important competitors for the adsorption sites of activated carbons during gold adsorption. In the present paper, an adsorption mechanism of negatively charged Cu cyanocomplexes on available sites of different activated carbons is proposed. The mechanism considers the (i) solution chemistry (e.g., effects of pH, CN/Cu molar ratio, and ionic strength by adding Na + , K + , and Ca 2 + cations); (ii) surface properties of the activated carbon samples (e.g., density of surface functional groups and point of zero charge — PZC); and (iii) copper speciation. The adsorption experiments demonstrated that the enhanced interaction of copper species at pH PZC > pK a basic groups ), electrostatic repulsion inhibits the adsorption of negatively charged Cu species. It is also proposed that the interaction of Ca 2 + ions with acid groups generate an excess of locally positive charges on the surface of the activated carbon, and such positive charges enhance the adsorption of negatively charged copper cyanocomplexes, even when the net surface charge is negative. The results from thermodynamic and Raman analyses indicated that under typical, practical conditions of gold adsorption from cyanide solutions (pH > 9 and CN/Cu molar ratio > 4), the main competitor for the adsorption sites of the activated carbon is the Cu(CN) 3 2 − species and not the Cu(CN) 2 − species.