Ammoniacal Carbonate Solution Research Articles

Validation and Implementation of Cold Purification Cake Leaching in Ammoniacal Carbonate Solutions at Hindustan Zinc Hydro Refineries

Cold purification cake generated during the purification of zinc leachate mainly contains copper 30–40% along with zinc 10–20% and cadmium up to 2%. Photomicrographs of purification cake indicated the major presence of copper in metallic/oxidized form. In the present work, ammoniacal carbonate leaching of purification cake followed by solvent extraction using diketone-based solvent has been studied under the influence of various parameters, viz. temperature, agitation, pulp density, ammonia, CO2 dosages, solvent concentration and impact of w/s zinc on leaching and solvent extraction. Leaching kinetics were determined based on shrinking core model. Chemical reaction at unreacted core was found to be the rate controlling step. The estimated activation energy was found to be 24 kJ/mol. Leached copper was extracted by solvent extraction with a β-diketone-based solvent and was stripped with sulfuric acid as concentrated copper sulfate solution. The above-established R&D findings were successfully implemented in the commercial plant with a treatment capacity of two tons of cold purification cake per batch.

Electrochemical behaviour of Ni3S2 and its spontaneous formation on metallic iron in ammoniacal-carbonate solutions

The oxidative dissolution of iron in ammoniacal-carbonate solutions containing nickel(II) and thiosulfate ions was found to result in the formation of a nickel sulfide layer which, based on Grazing Incidence X-Ray Diffraction (GIXRD) studies conducted on the iron surface following immersion, was found to contain Ni3S2. Consistent with this, linear sweep and rotating disk cyclic voltammetry measurements conducted with the iron electrode following immersion in these solutions resulted in the presence of an anodic peak thought to correspond to the oxidation of the nickel sulfide layer. Different concentrations and relative ratios of the ammonia and carbonate species were found to have a significant effect on both the size of this anodic peak, as well as the electrochemical behaviour of the iron during the immersion period under open circuit conditions. The results suggested that an increase in total carbonate concentration relative to the total ammonia concentration promoted the formation of the nickel sulfide layer which, in more dilute solutions than those typically encountered in industry, was in turn found to promote passivation of the iron. In order to evaluate the re-dissolution behaviour of the nickel sulfide layer following its potential formation on iron, further investigations were conducted using commercial Ni3S2, which was found to have a similar XRD pattern and electrochemical behaviour to the nickel sulfide layer formed on iron. Electrochemical studies indicated that the dissolution of Ni3S2 in ammoniacal-carbonate solutions is likely to be limited by the formation of a nickel-deficient, sulfur-rich species.

Validation and Implementation of Cold Purification Cake Leaching in Ammoniacal Carbonate Solutions at Hindustan Zinc Hydro Refineries

As a part of regular purification process for zinc leachate, cold purification cake is being generated at Hindustan Zinc refineries. Since the cake is being accumulated as an inventory, a treatment process has been designed to recover the copper in house and utilize it as an activator in zinc flotation circuit. It majorly contains copper (30-40%) along with zinc (10-20%) and cadmium (2%). With confirmation to the above statement, photomicrographs of purification cake also confirmed the major presence of copper in metallic or oxidized form. In present work ammoniacal carbonate leaching of purification cake followed by solvent extraction using diketone based solvent has been studied under the influence of various parameters viz., temperature, agitation, pulp density, ammonia, CO₂ dosages, solvent concentration, and impact of w/s zinc on leaching and solvent extraction. Leaching kinetics determined based on shrinking core model. Chemical reaction at unreacted core was found to be the rate controlling step. The estimated activation energy was found to be 24 KJ/mol. Leached copper has been extracted by solvent extraction with a β diketone based solvent and is stripped with sulfuric acid as concentrated copper sulfate solution. The above established R&D findings are successfully implemented in the Commercial plant with a treatment capacity of two tons of cold purification cake per batch.

Comparative study of organic solvents for extraction of copper from ammoniacal carbonate solution

Ammoniacal leaching followed by solvent extraction is practiced for the production of copper sulfate from copper dross generated in lead refinery during the pyro metallurgical production of lead. Copper is leached from its dross as Tetra-amino-Copper (II)-carbonate complex in the solution. Copper leached solution is guided through the solvent extraction process, using LIX-54 as a solvent and sulphuric acids as stripping agent to generate copper sulfate solution of the desired grade. Due to limited availability of LIX-54, performances of other solvents having a base of cinnamate and β diketone groups are evaluated. Both the solvents and LIX-54 have been compared in fields of effective organic concentration, effective loading, extraction kinetics, extraction isotherms, stripping activity and the optimized values are 20% organic concentration, 20g/l Cu, 35s, one theoretical stage for extraction and stripper acidity of 120g/l respectively. Under these conditions, >98% of copper has been extracted.

The anodic dissolution of iron in ammoniacal–carbonate–thiosulfate–copper solutions with formation of Cu2S and dendritic copper

The presence of thiosulfate ions in ammoniacal–carbonate solutions containing copper(II) ions was found to prevent the passivation of iron, even though iron passivation is observed in solutions with no thiosulfate at very low copper(II) concentrations. The prolonged anodic dissolution of iron resulted in the formation of a partly crystalline sulfide layer on its surface, which based on Grazing Incidence X-Ray Diffraction (GI-XRD) analysis is thought to consist mainly of Cu2S. The effect of the sulfide layer was investigated using rotating disk cyclic voltammetry. Unlike the formation of an amorphous CoSx layer, which took place in similar solutions containing cobalt ions, the cuprous sulfide layer was not found to promote passivation of the iron. A significant amount of solid precipitate also became detached from the iron surface, remaining undissolved in the solution. This was analysed by X-Ray Diffraction (XRD) and scanning electron microscopy (SEM)–energy dispersive X-ray spectroscopy (EDX). Dendritic copper was observed both in the solid separated from the solution and in the precipitate still attached to the iron surface. The absence of iron passivation is thought to be due to both to the non-adherent nature of the cuprous sulfide layer, and to a disrupting effect caused by the cementation of copper.

An electrochemical investigation of the formation of CoSx and its effect on the anodic dissolution of iron in ammoniacal-carbonate solutions

It has been found that the co-presence of cobalt (II) and thiosulphate ions in ammoniacal-carbonate solutions promotes the passivation of iron, under conditions in which it would otherwise continue to dissolve anodically. Electrochemical experiments have shown a relationship between the immersion time required for passivation and the formation of a solid species on the iron surface, which is thought to be implicated in the mechanism of passivation, whilst not being itself the protective species. Based on a combination of electrochemical, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and grazing incidence X-ray diffraction (GIXRD) characterisation techniques, the said species has been identified as CoSx, resulting from the interaction of cobalt (II) and thiosulphate ions. It is thought to form as a product of the cathodic reactions taking place on the iron surface during its active dissolution.These findings are particularly relevant to the Caron process, in which the ammoniacal-carbonate solutions containing dissolved cobalt and thiosulphate ions are used to leach nickel and cobalt from pre-reduced laterite ores rich in metallic iron. Both the loss of cobalt into the CoSx layer and the passivation of iron and of its alloys with nickel and cobalt, are potential contributing factors to the low cobalt and nickel recoveries, which are typical of the Caron process. This study provides a better understanding of the conditions under which the CoSx layer forms and promotes the passivation of iron, and may therefore provide useful information to help minimise the effect this may have on the extraction efficiency of the process. In particular, at the cobalt and thiosulphate ion concentrations usually encountered at a Caron plant, the passivation of iron was found to be prevented by maintaining a high enough concentration of ammonia.

Cobalt loss due to iron precipitation in ammoniacal carbonate solutions

Restrictions in the proportion of recoverable cobalt from laterite ores in the Caron process are attributed to multiple effects. One of these is adsorption of cobalt solution species on the precipitated iron oxide phase. Cobalt loss to an iron oxide precipitate produced in an ammoniacal carbonate solution was investigated. Adsorption experiments, both during and after iron precipitation, were conducted under a variety of process conditions. While prior research has focused more on cobalt adsorption on hematite, the primary phase present in the residue was found to be ferrihydrite. Based on significant differences in adsorption capacity between various iron oxide phases, the material present in the residue will make a significant difference in cobalt losses. Cobalt loss was minimised at low iron concentrations, pH 10 and high ammonia concentrations, while temperature (over the range tested) did not display a significant impact on cobalt loss or the precipitated phase.

Geochemistry of arsenic and metals in stored tailings of a Co–Ni arsenide-ore, Khovu-Aksy area, Russia

Abstract Interest in the redistribution of As-bearing species during long-term storage of hydrometallurgical tailings is motivated partly by the need to prevent As from being released into the environment. The speciation of As in mine wastes from the Tuva Cobalt Plant (Khovu-Aksy mine site, Tuva Republic, Russia) has been studied using mineralogical techniques, and chemical analyses of solids (tailings, soils, vegetation) and solutions (recovered pore waters, leach solutions). Ore at the plant was processed by hot autoclave leaching with an ammoniacal carbonate solution followed by treatment with CO2(gas) and caustic magnesite, MgO. Pronounced differences in element concentrations were measured in the five separate tailings ponds and one trench that were filled sequentially during operation of the plant. The concentration of each element was relatively uniform within each pond but the correlations among solid-phase Co, Ni, Zn and Cu gradually decrease from the most recent to oldest ponds as does the correlation between solid-phase As, Ag, Cd and Pb. In the oldest ponds, significant correlations are present between solid-phase Fe–As, Fe–Sb and Fe–Zn. High carbonate content in the ores and leaching reagents control the pH of the pore waters (pH = 7.27–9.10) where the major cation is Ca2+, followed by NH 4 + and Mg2+. Concentrations of As in pore solutions reach up to 140 mg L−1, and average 15 mg L−1. The high pore-water As concentrations are a consequence of instability of the processing residues, which include Mg(NH4)AsO4⋅nH2O and Mg3(AsO4)2⋅nH2O. The concentrations of Zn, Cu and As in pore waters increase from the youngest pond to the oldest storage impoundment (trench), which is evidence of the increase in element mobility with time. In contrast to the metals, As is preferentially sorbed to Fe oxides formed in the tailings. Aerosol transport of dust from the dry ponds has produced anomalies of As and metals in the surrounding area with As in the most polluted soils reaching up to 540 ppm. Moreover, vegetation growing on the surface of the disposal ponds absorbs solutes from the soil.

The Electrochemistry of the Leaching Reactions in the Caron Process. I. Anodic Processes

The Caron process involves the oxidative dissolution of pre-reduced iron alloys containing nickel, cobalt and copper in ammoniacal carbonate solutions. This study has demonstrated that passivation is exhibited by nickel and cobalt at higher potentials than previously established for iron. It is shown that alloys of iron with nickel and cobalt also undergo passivation at low potentials resulting in inhibition of the dissolution of the valuable metals. The potential regions of active dissolution of each of these metals in ammonia-ammonium carbonate solutions have been established. The effect of thiosulphate and cobaltammine complex ions on the dissolution of iron and nickel was found to be significant in that thiosulphate appears to partially prevent the passivation of nickel while the presence of cobaltammine ions leads to lower apparent anodic current densities. Possible mechanisms for the passivation processes and for the effects of thiosulfate and cobaltammines on the dissolution are presented.

Separation of Copper and Nickel from Ammoniacal/Ammonium Carbonate Solutions Using ACORGA PT5050

ABSTRACT ACORGA PT5050 diluted with iberfluid (kerosene-type diluent, mostly aliphatic) was used to coextract copper and nickel from ammoniacal carbonate solutions. The influence of kinetics, temperature, equilibrium pH, and extractant concentration on the extraction of both metals has been studied. It was observed that nickel extraction is very sensitive to aqueous pH and that the extraction falls beyond an equilibrium pH of 9. For a typical solution containing near 3 g/L each of copper and nickel and 60 g/L ammonium carbonate, conditions were established for the coextraction and selective stripping of nickel and copper.

Co-extraction and selective stripping of copper and nickel using LIX87QN

LIX87QN diluted with kerosene (mostly aliphatic) was used to co-extract copper and nickel from ammoniacal carbonate solutions. The influence of equilibrium pH and extractant concentration (in the organic phase) on co-extraction has been studied. It was observed that nickel extraction is very sensitive to equilibrium pH and that the extraction falls sharply beyond an equilibrium pH of ∼ 9. For a typical solution containing about 3 kg/m 3 each of copper and nickel and 60 kg/m 3 of ammonium carbonate, conditions were established for the co-extraction, NH 3 removal, and selective stripping of nickel and copper. The percentage of extraction was ∼ 100 for both copper and nickel. The percentage of nickel stripping was 99.2 and that of copper was ∼ 100.

Anodic Behavior of Iron in Ammoniacal Carbonate Solution: I . Steady‐State Polarization and Cyclic Voltammetry

Two distinct Tafel regions are observed in the active region of the anodic polarization curve of iron in ammoniacal carbonate solution. A prepassive layer may form in the Tafel region at the higher overpotentials. A hydrogen oxidation peak is proposed to occur in the lower overpotential Tafel region. Anodic dissolution of iron in both Tafel regions is under mixed surface and diffusion control. The passivation of iron in ammoniacal solution involves charge transfer followed by a rate controlling chemical step. The stability and/or thickness of the passive layer and the Fe(III)/Fe(II) ratio increase with more noble potentials in the passive region.

Investigation of deactivation mechanisms of ASC whetlerite charcoal

ASC whetlerite, prepared by the impregnation of CWS grade activated charcoal with ammoniacal carbonate solutions of copper(II), chromium(VI), and silver salts, is an effective material for the removal of many low-molecular-weight gases (e.g., cyanogen chloride and hydrogen cyanide) from air streams. Whetlerite loses its effectiveness when exposed to extremes in temperature and/or humidity or by excessive periods of usage. Associated with this deactivation/deterioration process are changes in metal oxidation state(s) and impregnant morphology. This investigation examines the behavior of the metal impregnants on ASC whetlerite when subject to certain extreme conditions and, as a result, develops an understanding of the deactivation mechanism(s) that occur. The deterioration of whetlerite due to thermal deactivating conditions as well as that due to exposure to hydrogen involves the decomposition of the supported CuOHNH 4CrO 4 (basic copper ammonium chromate) species. This complex chromate decomposes into a CuOCuCr 2O 4 (copper-chromite) species upon thermal treatments up to 490 K. At temperatures above 490 K the CuO (cupric oxide) sinters away from the chromite and is subsequently reduced to Cu 1+-containing and Cu 0 species. When exposed to high humidities for long periods of time (i.e., more than 2 days) it is hypothesized that the whetlerite surface experiences a decrease in pH. This results in the supported CuOHNH 4CrO 4 species converting to Cu 4(OH) 6CrO 4 (brochantite chromate). The brochantite chromate gradually decomposes into less complex crystalline compounds such as CuO, Cu 2Cr 2O 4, and Cr 2O 3 which are not effective for destroying irritating gases.

Adsorption of cobalt by lignite

Studies similar to earlier ones which had established the feasibility of extracting nickel by the lignite adsorption route were conducted on the adsorption extraction of cobalt on lignite, and with equal success. Optimal values of variables such as pH, sorbent/sorbate ratio, adsorbent particle size, contact time, temperature, and the effect of excess ammonium carbonate were evaluated. The rate of adsorption of cobalt was found to be slower than that for nickel. However, the recovery of over 99% cobalt from ammoniacal carbonate solutions, at optimal conditions, was comparable to that for nickel. The cobalt was recoverable as metal, by ignition of the loaded lignite, or in solution, by elution with sulfuric acid in single or multiple stages.

Absorptiometric Determination of Micro-amounts of Iron in Nuclear Grade Graphite and Urania-Graphite Fuel; Nitroso R Salt Method after Coprecipitation of Iron with Manganese Dioxide

Abstract An absorptiometric determination of micro-amounts of iron with nitroso R salt was satisfactorily applied to the routine analysis of nuclear grade graphite. An ashed sample is brought into a solution and the color of iron is developed by the reagent with the aid of hydroxylamine sulfate. Adjustment of pH to the optimum range is easily made by the addition of a definite amount of an acetate buffer. The intensity of the color is measured at 715 mμ. The range of the determination covers 2 to 75 p. p. m. when 1 g. of a sample is taken, the final volume being 25 ml. In the case of a sample of urania-graphite fuel, the ash is fumed with perchloric acid and a preliminary separation is made by coprecipitation with manganese dioxide which is produced by the oxidation of manganese (II) ion with hydrogen peroxide in a hot ammoniacal carbonate solution. The recovery of iron is quantitative and the removal of diverse ions is satisfactory. All of the uranium is also removed here. Contamination with foreign iron from a drill used for sampling and from the platinum or percelain crucibles used is negligible. The effect of diverse ions on the absorptiometry was also examined.