Ammoniacal Ammonium Carbonate Research Articles

Leaching of synthetic Ca3WO6 with ammoniacal ammonium carbonate solution under atmospheric pressure: A fundamental study

In (NH4)2CO3 solution, leaching Ca3WO6-bearing product converted from tungsten concentrate can directly obtain ammonium tungstate solution, and thus eliminates high-salinity wastewater discharge in ammonium paratungstate manufacture. Possible reactions of Ca3WO6 leaching in aqueous ammoniacal ammonium carbonate solution under atmospheric pressure were investigated thermodynamically and experimentally. The results show that tungsten in Ca3WO6 can be efficiently leached out by forming CaCO3(s) and (NH4)2WO4 (aq) in aqueous ammoniacal ammonium carbonate solution, while raising ratio of total ammonia to total carbon in solution and forming calcite are beneficial to increase the WO3 leaching ratio. Whereas the secondary reactions of Ca3WO6 with H2O and/or Ca (OH)2/CaCO3 with (NH4)2WO4 may occur and thus CaWO4 forms in the leaching, decreasing WO3 leaching ratio especially in concentrated (NH4)2WO4 solution and in case of forming vaterite. In addition, a three-layer cover was observed on the unreacted Ca3WO6 and hinders the leaching process. Through simultaneous grinding and leaching, both high WO3 leaching ratio and high WO3 concentration leachate can be achieved by increasing ratio of total ammonia to total carbon in NH3-(NH4)2WO4- (NH4)2CO3-H2O system. These results are helpful to optimize the leaching process of the converted product with Ca3WO6 by roasting tungsten-containing materials.

Sustainable and efficient leaching of tungsten in ammoniacal ammonium carbonate solution from the sulfuric acid converted product of scheelite

Abstract To directly obtain solution of (NH4)2WO4 instead of Na2WO4 is the key for developing a cleaner technology of ammonium paratungstate production. In this paper, ammoniacal ammonium carbonate solution was adopted for leaching tungsten from the converted product, a mixture of H2WO4 and CaSO4 obtained by treating scheelite with sulfuric acid. The research indicates that tungsten can be efficiently extracted in form of ammonium tungstate solution with WO3 leaching yield of >99.5% under moderate leaching conditions. The WO3 leaching yield is influenced by the transformation of calcium sulfate to calcium carbonate due to forming CaWO4 through the secondary reaction between CaSO4 and (NH4)2WO4, whereas an excess (NH4)2CO3 (≥0.64 mol/L) can suppress the secondary reaction by facilitating the transformation. Additionally, the consumed ammonium carbonate can be recovered by treating the leaching residue with ammonium sulfate solution at above 70 °C. This work presents a cleaner and sustainable technique for producing ammonium paratungstate, with circulating the leaching reagents and bypassing the conversion of Na2WO4 to (NH4)2WO4.

Synthesis and microstructural properties of zinc oxide nanoparticles prepared by selective leaching of zinc from spent alkaline batteries using ammoniacal ammonium carbonate

Two different precursors of zinc oxide were prepared via the ammoniacal ammonium carbonate leaching of the black mass obtained during the recycling of alkaline batteries. For a concentration of 0.1 mol/L of ammonium in the leaching solution, zinc basic carbonate, was obtained, while for higher ammonium concentrations (0.5 and 1 mol/L), zinc ammonium carbonate was the final product. These precursors were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA/DTG) and Scanning electron microscopy (SEM), and calcined to obtain ZnO. Raman spectroscopy, X-ray diffraction and Transmission electron microscopy (TEM) analysis of the resulting zinc oxide samples indicated a wurtzite hexagonal lattice with a parameter values ranging from 3.23 Å to 3.30 Å, and c parameter values from 5.18 Å to 5.21 Å (values close to typical). The room temperature photoluminescence spectra of the zinc oxide samples showed two main bands: a high energy UV-blue band centred at either 412 or 382 nm (depending on the NH3 concentration of the leaching solution used), and a green band centred at 527 nm. These emission bands are comparable to those reported for pure zinc oxide.

The Study on the Crystallization Conditions of Zn5(OH)6(CO3)2 and its Effect on Precipitation of ZnO Nanoparticles from Purified Zinc Ammoniacal Solution

The authors studied the crystallization conditions and formation mechanism of zinc carbonate hydroxide [Zn5(OH)6(CO3)2] based on the crystallization theory. An ammoniacal ammonium carbonate zinc aqueous solution was employed for this aim. After achieving the maximum solubility of zinc in ammonium carbonate solution by controlling its pH and temperature (85°C and pH = 9.5), the crystallization conditions were performed by both diluting with water and heating the saturated solution. The results showed that heating of saturated solution is more practical than diluting with water. The conversion of Zn5(OH)6(CO3)2 to ZnO was carried out by calcination at 400°C for 2 h, based on its decomposition temperature obtained from TGA-DTA analysis. TEM images of obtained the ZnO powder showed that discrete nanoparticles (with the size of about 50–60 nm) were formed after calcination process. The techniques of SEM, TEM, STA, XRD, BET, and Raman spectroscopy were applied for the characterization of the produced materials.

Thermochemistry of the Fe, Ni and Co-NH3-H2O systems as they relate to the Caron process: a review

Passivation of Fe-Ni-Co alloys during the Caron leach process is thought to result in low cobalt recoveries in ammoniacal ammonium carbonate solutions. A brief review of the available thermochemical data for the (Fe, Ni, Co)-NH3-H2O systems has been undertaken. The stability of the Co(II) and Co(III), Ni(II) and Fe(II) ammines was examined through the use of speciation and Pourbaix diagrams at 298 and 333 K and at 6 M total ammonia. Increasing the temperature reduces the stability fields of the ammines and generally constrains the thermodynamic window for the leach. The Fe(II) ammines are only thermodynamically stable under reducing conditions. Polarization experiments show that these ammines are unlikely to form if oxygen is present. Fe-Ni-Co alloy passivation may be alleviated by careful management of potential.

Selective Leaching of Zinc from Spent Zinc-Carbon Battery with Ammoniacal Ammonium Carbonate

This paper describes the ammoniacal ammonium carbonate leaching behavior of zinc and manganese from spent zinc-carbon batteries. For selective extraction of Zn from the spent zinc-carbon battery, leaching tests were carried out as a function of process parameters such as concentration of (NH4)2CO3, ammonia, temperature, time and pulp density. Physical methods of separation such as crushing was applied to reduce the material to 10–20 mm size followed by magnetic separation to separate iron with a recovery about 10 mass% leaving most of Zn and Mn in the non-magnetic fraction. Non-magnetic fraction was further subjected to sieving to separate 2.46 mm over and under size fractions. The oversize material was processed by eddy current separation to recover zinc sheet and carbon rods and plastics. The under size material with chemical composition of Zn 15.5 mass%, Mn 17.5 mass%, and Fe 1.4 mass% was used for leaching studies. Under the optimum leaching conditions (2.0 kmol/m 3 (NH4)2CO3 and 4.0 kmol/m 3 ammonia, 40 � C, 100 g/L pulp density, 30 min and 250 rpm), the leaching efficiency of zinc and manganese was 80.2% and less than 0.1%, respectively, indicating the selective recovery of zinc from the spent zinc-carbon battery. An overall zinc recovery is about 88%. [doi:10.2320/matertrans.MRA2008164]

Purification of zinc ammoniacal leaching solution by cementation: Determination of optimum process conditions with experimental design by Taguchi's method

The Taguchi method was used as the experimental design to determine the optimum conditions of purification behavior of the leach solution obtained from ammoniacal ammonium carbonate leaching of nonsulphide zinc ores in Angoran region (Iran). Cementation was performed using zinc dust. The experimental conditions were studied in the range of 25–65 °C for reaction temperature ( T), one to five series for zinc dust particle size distribution ( S), 15–75 min for reaction time ( t), 0.3–1.6 g/l for zinc dust value ( M), and 300–500 rpm ( R) for stirring speed. Experimental parameters and their levels were determined in the light of preliminary tests. Orthogonal array (OA) L 25 (5 5) consisting of five parameters each with five levels, was chosen. The total optimum purification conditions obtained from this study were T2 (35 °C), S1 (series 1), t3 (45 min), M5 (1.6 g/l), and R4 (450 rpm), respectively. In these conditions, all of the impurities (cadmium, lead, nickel, and cobalt) were completely removed.

Ammonium carbonate leaching of carbon steelmaking dust. detoxification potential and economic feasibility of a conceptual process

Dumping of untreated dust generated during electric arc furnace (EAF) carbon steelmaking is nowadays regarded as hazardous practice. This is due to the presence in the material of toxic species leachable under mildly acidic conditions. The use of ammoniacal ammonium carbonate (AAC) leaching for the treatment of EAF dust has been investigated on a laboratory scale and is reported in this paper. The experiments were conducted on dust samples from three European companies. As received, the dusts were found to be toxic when tested according to current US Environmental Protection Agency (EPA) toxicity testing procedures. Toxicity was on account of the leachability of one or more of the following: Ag, Hg, Pb, and Cd. For the three dust samples, it has been found that AAC leaching is able to rapidly solubilize the contained free zinc oxide to yield non-toxic residues according to EPA criteria. On the basis of the bench scale results obtained, a process is proposed for the treatment of EAF dust by AAC leaching. A preliminary economic appraisal of the proposed process is presented which indicates that AAC leaching has a potential of being a competitive alternative to current dust treatment technologies.

Active and passive behavior of sintered iron in ammoniacal ammonium carbonate solution

The anodic dissolution behavior of sintered iron in ammoniacal ammonium carbonate solution (pH = 9.7) has been investigated with the aid of electrochemical techniques. Surface films formed on bulk iron during air exposure or immersion in the ammoniacal solution were characterized by using X-ray photoelectron spectroscopy (XPS). Immersion in the ammoniacal solution gave an apparent open circuit potential (OCP) in the range ofE = 0.04 to 0.09 V, standard hydrogen electrode (SHE); at these potentials, no dissolution of Fe was detected. Potential transients obtained during cathodic reactivation and the XPS results suggest that an air-formed oxide of Fe3O4 is responsible for this behavior. The anodic polarization behavior of sintered Fe was similar to that of bulk Fe, showing active, passive, and oxygen evolution regions. A very high current density observed in the passive region for some sintered specimens was attributable to active dissolution within the pore structure, analogous to conditions during crevice corrosion. The presence of oxygen in the solution stabilized both the passive film and the more noble apparent OCP.

Leaching of roast-reduced polymetallic sea nodules to optimise the recoveries of copper, nickel and cobalt

The reduction-roasting ammoniacal-leaching technology, widely used for the processing of nickel laterites, has been applied for the extraction of copper, nickel and cobalt from polymetallic sea nodules of the Indian Ocean. Results are presented of the various leaching experiments conducted under different conditions to optimise the recoveries of copper, nickel and cobalt. Leaching of the ground roasted product was carried out in ammoniacal ammonium carbonate solution. The effect of preconditioning of the reduced nodules in strong ammoniacal solution prior to leaching was studied. The leaching behaviour of the metals after grinding the roasted product in air, water, leachant and preconditioning solution was carefully examined. Air grinding of the roasted product, preconditioning and leaching was found to give the best recoveries of copper, nickel and cobalt. Cobalt was recovered to a maximum of about 60% in 2 h, but dropped to 40% at the end of 4 h of leaching. Based on these observations, a two-stage leaching scheme (each stage of 2 h duration) was devised to optimise the recoveries of all the three metals, which has yielded copper, nickel and cobalt recoveries of 91%, 94% and 62%, respectively.

Extraction of nickel and copper from the ammoniacal leach solution of sea nodules by LIX 64N

Studies on the extraction of nickel and copper from the ammoniacal ammonium carbonate solution were undertaken using LIX 64N as an extractant. The solvent showed preference for extraction of copper over nickel from the ammoniacal solutions. The leach liquor of sea nodules from the Indian Ocean was processed in a laboratory-size mixer-settler unit by coextracting nickel and copper in 20% LIX 64N in kerosene. The extracted ammonia from the. solvent was removed by scrubbing with ammonium bicarbonate and dilute sulfuric acid. 'Nickel was selectively stripped with the spent electrolyte of 1.75 pH, and the strip solution was purified with a stream of LIX 64N to remove the residual copper. Copper was subsequently stripped with spent electrolyte containing 170.5 g/L sulfuric acid. These strip solutions were found to have an appropriate amount of acid for electrowinning the metals.

Anodic Dissolution of Iron in Ammoniacal Ammonium Carbonate Solution

The electrochemical behavior of iron has been characterized in aqueous ammoniacal ammonium carbonate solution. Pure iron anodically polarized in He‐ or solutions exhibits both stable active (, SHE) and passive regions. A cathodic loop was observed in the potential range of −380 to 100 mV. It is suggested, on the basis of cathodic polarization curves of a graphite electrode in various concentrations of ammoniacal solution, that the cathodic loop is due to oxygen discharge. The addition of to the ammoniacal solution has the same effect as oxygen in that it increases the cathodic current and potential range of the cathodic loop and, as such, functions as a strong oxidant.

Cobalt extraction in ammoniacal solution: Electrochemical effect of metallic iron

The dissolution behavior of iron and cobalt in ammoniacal ammonium carbonate solution has been investigated with the aid of Eh-pH diagrams for the Fe-NH3-H2O-CO3 and Co-NH3-H2O-CO3 systems, and electrochemical techniques such as open circuit potential measurements and potentiostatic and potentiodynamic polarization experiments. The polarization measurements indicate that both Fe and Co electrodes show active and passive behavior, and that Co dissolves at a more oxidizing potential than does Fe(e.g., E = −0.34 V (SHE) for Co andE = −0.52 V for Fe at a dissolution rate of 1 mA cm−2). The active and passive current densities for Co are both greater than for Fe. In sintered Fe-Co mixtures, the presence of Fe shifts the potential of the maximum current to less noble values and also lowers the magnitude of this current. In addition there is practically no cobalt dissolution when the potential exceeds 0.6 V (SHE). It is suggested that the well-known poor recovery of cobalt from reductive-roasted ferruginous oxide ores may be partly related to the dissolution behavior of a metallic alloy phase containing both iron and cobalt.