The behavior of arsenic trioxide in non-ferrous extractive metallurgical processing

pre-printStudy of the acid bake-leach process has shown potential advantages for the treatment of enargite (Cu3AsS4) concentrates. Among the most important advantages of the process is the transformation of enargite to water-soluble copper sulfate and highly soluble arsenic trioxide (arsenolite). Because arsenic is retained in the condensed phase during the baking, the vapor pressure of arsenic trioxide should be estimated at typical baking temperatures (e.g. 473 K). To that end, the vapor pressure of As4O6 (g) was estimated under the baking conditions based on published thermodynamic values. The vapor pressure of arsenolite at 473 K was found to be approximately 9.03 x 10-4 atm. Based on the linear regression analysis of the published vapor pressure values for arsenolite in the temperature range 366-579 K, the equation for the best fit line was found to be as follows, with a correlation coefficient of 0.9973: Available information on arsenic trioxide does not allow a definite conclusion regarding the arsenolite/claudetite transformation temperature and their exact melting points. However, the transition temperature has been reported to be in the wide range of 240-506 K in different references. Furthermore, the thermodynamic information concerning arsenolite/ claudetite is sparse and at times not consistent. An effort has been made in this paper to compile the most reliable thermodynamic information for arsenic trioxide (arsenolite and claudetite)

Recent Trends in the Processing of Enargite Concentrates

The copper industry is witnessing great interest in the development and utilization of copper-arsenic deposits. While most plants tend to use traditional processing technologies, the depletion of conventional copper ores has created competition for designing and implementing new process alternatives for the treatment of copper-arsenic ores containing minerals such as enargite, luzonite, and tennantite. Nevertheless, the downstream processing of high-arsenic copper concentrates represents a significant metallurgical challenge in terms of both arsenic separation and also its stabilization in an environmentally benign form that fulfills the current and future environmental policies. Smelters are subject to penalties on high arsenic-bearing copper concentrates. While reductive roasting can drive-off the arsenic from enargite concentrates to an acceptable level suitable for smelting ( \u3c 0.5 wt.%), this option has generally been viewed as unacceptable due to environmental conflicts and the lack of a market for arsenic trioxide. The lack of a suitable pyrometallurgical option has led to several proposed hydrometallurgical treatments of enargite concentrates. Hydrometallurgical options include either selective arsenic dissolution to produce a clean copper concentrate or collective leaching of copper and arsenic. Both options with various conditions and lixiviants are discussed and evaluated. In this review, alkaline sulfide leach (ASL), sulfate-and chloride-based leach systems, high temperature pressure oxidation (HTPOX), sodium hypochlorite leach, bio-leach/oxidation, nitrogen species catalyzed pressure oxidation, Cominco Engineering Services Limited, Intec, HydroCopper™ and Fluobor® processes are outlined. Pyrometallurgical process strategies have also been briefly reviewed. Among all processing options, ASL, HTPOX, Fluobor® and reductive roasting processes are given special attention with specific flowsheets for enargite concentrates discussed

An Update to Recent Trends in the Processing of Enargite Concentrates

An update is presented to the paper Recent trends in the processing of enargite concentrates by Safarzadeh, Moats, and Miller (2014). Publications which were not included in the initial review paper, primarily to avoid redundancy, are presented and discussed here. Thus, roasting, atmospheric acidic and alkaline leaching, the dissolution of enargite in low-melting point salts, bioleaching, and pressure leaching are presented. For the first time, the modified phase stability (Kellogg) diagram and the Eh-pH diagram for the Cu-As-S system including sinnerite (Cu6As4S9) have been established. According to the results from different treatment options discussed in our earlier review and also in this paper, it is evident that the most recent research activities for the treatment of enargite concentrates are centered around roasting, alkaline sulfide leaching, and high temperature pressure oxidation. Taking into account the advantages and disadvantages of the mentioned processing options, and the numerous preliminary experiments performed, the acid bake-leach process has been identified and is being studied at the University of Utah. It has been found that enargite transforms to water-soluble copper sulfate, arsenic trioxide and elemental sulfur by sulfuric acid baking of enargite at 200°C, with less than 1% of the arsenic being released to the gas phase. This process strategy provides a new possibility for the treatment of enargite concentrates

Acid Bake-Leach Process for the Treatment of Enargite Concentrates

As an alternative to roasting, low-temperature (100-200 °C) sulfuric acid baking of an enargite concentrate followed by water-leaching has been evaluated. Results indicate the thermal transformation of enargite and pyrite during sulfuric acid baking. by acid baking of an enargite concentrate at 200 °C for 7 h, ~ 90% Cu and ~ 61% as were released to the leach solution, with \u3c 1% of arsenic being released to the gas phase. The effects of time and temperature were studied on the baking reactions. Extended reaction times (24 h) at lower baking temperatures (170 °C) resulted in lower Cu and as extraction and higher as release to the gas phase (~ 11%). The pH of the water leach solution was always ~ 0.8-2 after extraction due to residual acid, making it suitable for subsequent copper recovery. The oxidation-reduction potential (ORP) of the leach solution fell within the range 491-566 mV (vs. SHE) depending on the baking conditions. The ratio of ferric/ferrous ions in the leach solution showed considerable dependence to reaction time and temperature. Based on this study, some reactions are proposed for the sulfuric acid baking of enargite

Erratum: Acid Bake-Leach Process for the Treatment of Enargite Concentrates (Hydrometallurgy (2012):119-120 (30-39))

Reactions (6) and (9) on pages 36-37 are corrected as follows

The Stability of Selected Sulfide Minerals in Sulfuric Acid and Acidic Thiocyanate Solutions

The stability of pyrite, chalcopyrite, chalcocite, covellite, bornite and enargite at pH 2 in the absence and presence of thiocyanate has been determined by linear sweep voltammetry and chronoamperometry under conditions pertaining to the thiocyanate leaching of gold (pH 2 and 602-702 mV vs. SHE). Electrochemical measurements indicated that the decomposition rate of all sulfide minerals increased with an increase in oxidation potential with pyrite and chalcopyrite being the least reactive and chalcocite and bornite being the most reactive of the examined sulfides. The oxidation rate of covellite and enargite was higher than that of pyrite and chalcopyrite but much lower than that of chalcocite and bornite. It was found that the variation of pH from pH 1 to pH 3 has minimal effect on the oxidation rate of pyrite and chalcopyrite. In the presence of 0.05 M thiocyanate at pH 2 and in the potential range of interest for gold leaching (602-702 mV vs. SHE), the effect of thiocyanate was not significant on the oxidation of selected sulfides

Understanding the Agglomeration Behavior of Nickel Laterite and Gold Ores using Statistical Design of Experiments

The drum agglomeration of nickel laterite and gold ores has been optimized through the design of experiments (DOE) using a Taguchi L16 (45) orthogonal array to determine the optimum conditions for maximizing average agglomerate size and minimizing the amount of fines. The effects of controllable operating factors including moisture content (nickel laterite ore: 34-37%; gold ore: 7-10%), retention time (2-3.5 min), drum speed (15-45% critical speed), drum load (nickel laterite ore: 8-32 %; gold ore: 6-22%) and acid concentration (150-600 g/L) on the performance of the agglomeration process were studied. For nickel laterite ore, maximum average agglomerate size and minimum percent fines (-1 mm) occurred under the following conditions: drum load (23.7%), moisture (36.5%), time (3 min), drum speed (30% critical speed) and acid concentration (150 g/L). Under the studied nickel laterite ore conditions, the most effective parameters for maximizing average agglomerate size and minimizing the amount of fines were found to be drum load and acid concentration, respectively. Drum speed had a statistically significant effect on minimizing the amount of fines. Maximum average agglomerate size and minimum percent fines (-1 mm) for gold ore occurred under the following conditions: drum load (19.3%), moisture (8.5%), time (2 min 15 s) and drum speed (40% critical). The most significant factors for maximizing average agglomerate size and minimizing the amount of fines for gold ore were found to be drum load, time and moisture

Crushed Ore Agglomeration and Its Control For Heap Leach Operations

Based on the extensive experience of heap leaching operations, crushed ore agglomeration can be successfully considered and utilized as a pretreatment step for the heap leaching of ores containing significant amounts of fines and clay minerals. The drum agglomeration is considered as a pretreatment step for the heap leaching of copper and gold ores whereas the agglomeration of uranium and nickel ores has received less attention over the past years. The acceptance of binder application for acidic leaching systems is limited primarily due to the lack of acid-tolerant binders. The use of binder depends mainly upon the cost considerations, impact on recovery and safe practice. of equal importance are the quality control and characterization tools for the agglomerates to ensure better heap performance. This paper attempts to provide a concise overview of available quality control and characterization tools for crushed ore agglomeration with industrial examples from the gold, copper, nickel and uranium operations. Consequently, different agglomeration-heap leaching systems and their differences are summarized. The requirements for effective agglomeration, characteristics for an ideal agglomerate and integrated flowsheet of crushed ore agglomeration-heap leaching system are discussed

Understanding the Agglomeration Behavior of Selected Copper Ores using Statistical Design of Experiments

The drum agglomeration of two different crushed copper ores (I and II) has been optimized using Taguchi\u27s L16 (45) orthogonal array design to determine the optimum conditions for maximizing the average agglomerate size and minimizing the amount of fines. The effects of controllable operating factors including moisture content (ore I: 9.6-11.1%; ore II: 12.8-14%), retention time (2-4 min), drum speed (15-45% critical), drum load (ore I: 13-32%; ore II: 6-24%) and acid concentration (6.5-90 g/L) on the performance of the agglomeration process were studied. For ore I, the maximum average agglomerate size and minimum percent fines (-1 mm) occurred under the conditions: drum load (22.75%), moisture (10.35%), time (4 min), drum speed (30% critical), and acid concentration (41 g/L), whereas for ore II, the same conditions occurred under the drum load (18%), moisture (13%), time (3 min), drum speed (30% critical), and acid concentration (30 g/L). Under the conditions studied for ore I, the most effective parameter for maximizing average agglomerate size and minimizing the amount of fines was found to be drum load. For ore I, time and acid concentration had a measurable effect on maximizing average agglomerate size, whereas moisture had a statistically significant effect on minimizing the amount of fines. For ore II, the most effective parameter for maximizing average agglomerate size and minimizing the amount of fines was found to be acid concentration. Time had a measurable effect on maximizing average agglomerate size, whereas the other variables did not affect the responses significantly for ore II