Enhanced Leaching of Zinc from Zinc-Containing Metallurgical Residues via Microwave Calcium Activation Pretreatment

Given the shortage of zinc resource, the low utilisation efficiency of secondary zinc resource, and the crucial problem that the synchronous dissolution of zinc from different mineral phases, an activation pretreatment method merged with calcium activation and microwave heating approach was proposed to enhance the zinc leaching from complex encapsulated zinc-containing metallurgical residues (ZMR). Results indicated that under the optimal pretreatment conditions, including microwave activation temperature of 400 °C, CaO addition of 25% and activation time of 20 min, the zinc leaching rate reached 91.67%, which was 3.9% higher than that by conventional roasting pretreatment. Meanwhile, microwave heating presents excellent treatment effects, manifested by the zinc leaching rates, all exceeding that of conventional roasting under the same conditions, while the process temperature is decreased by 200 °C. In addition, XRD and SEM-EDS analysis denoted that microwave calcification pretreatment can effectively promote the transformation of the refractory zinc minerals like Zn2SiO4 and ZnFe2O4 into the easily leachable zinc oxides. The distinctive selective heating characteristics of microwave heating strengthened the dissociation of mineral inclusion, and the generated cracks increased the interfacial reaction area and further enhancing the leaching reaction of zinc from ZMR.

Effective Removal of Barrier Layer on the Surface of Low-Nickel Matte in an FeCl3-HCl-H2O Solution

Using ferric chloride as an oxidant, here, we investigated the leaching effect of low-nickel matte in a flow field produced by mechanical agitation. The factors affecting a leaching reaction, such as stirring speed, leaching time, low-nickel matte particle size, and inert abrasive quartz sand, were studied. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), a laser particle size analyzer, optical microscopy (OM), a scanning electron microscopy (SEM) with an energy dispersive X-ray detector (EDS), and a Raman spectrometer were used to characterize the materials before and after the leaching reaction. The contents of the main metal ions such as Ni, Cu, and Co in the leaching solution were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Using the control variable method, the optimal experimental conditions were as follows: 2 mol/L FeCl3—0.5 mol/L HCl-H2O system with low-nickel matte and quartz sand (mass ratio is 1:5) and leaching at 90 °C for 8 h. The results showed that the blocking effect of the solid product sulfur layer was effectively removed and continuous leaching was realized. The leaching efficiencies of Ni, Cu, and Co were 98.9%, 99.3%, and 98.1%, respectively.

Rapid Atmospheric Leaching of Chalcopyrite Using a Novel Reagent of Trichloroisocyanuric Acid

With the decrease in high-grade chalcopyrite resources, the copper extraction from low-grade chalcopyrite has attracted more and more attention. However, the kinetic rates of chalcopyrite leaching with traditional oxidants are usually very slow due to the formation of the passivation layer. In this study, a novel reagent of chlorinated oxidant, trichloroisocyanuric acid (TCCA), was used to leach chalcopyrite for the first time. The experimental results showed that when the initial oxidant concentration for TCCA was 0.054 mol·L−1, the leaching temperature was kept at 55 °C, and the pH of the pulp was controlled at 1, the oxidation efficiency of Cu can reach above 90% in less than 30 min. Various analyses of chalcopyrite mineral ore and its oxidized residues, such as chemical composition analysis, X-ray diffraction analysis, scanning electron microscopy analysis and X-ray photoelectron spectroscopy, were conducted, respectively. No obvious passivation layer was found on the chalcopyrite surface, though the sulfur product can also be generated during the leaching. Reaction kinetic analysis results showed that the different influence of surface reaction and diffusion process on the dissolution of chalcopyrite is little due to the fast leaching speed. After calculation, the activation energy of the whole leaching reaction is 9.06 kJ·mol−1, much lower than that in other reports. The mechanism was also proposed that TCCA was hydrolyzed in the solution to form hypochlorous acid, which is the strong oxidant, and cyanuric acid, which prevents the formation of a passivation layer. The processing in this study is expected to be applied as a novel method for atmospheric leaching of chalcopyrite.

A Study on the Leaching of Rare Earth Elements from Waste Phosphor Powder

This study was carried out to obtain data to design a process to recover rare earth elements, specifically Y(Yttrium), La(Lanthanum), Ce(Cerium), Eu(Europium), Tb(Terbium) from waste phosphor powder. For this purpose, we investigated the effect of temperature, concentration, time and acids on leaching of the rare earth elements. The effect of roasting temperature, roasting time, roasting agent and its dosage on the leaching of rare earth elements were also investigated. 92% of the Yttrium, 70% of the Europium and 8% of the Cerium contained in the waste phosphor powder was leached at the condition of 50 oC and 0.3N HCl solution for 3hours. However, Terbium and Lanthanum were never leached at this condition. The leaching ratio increased to 100% of Yttrium and Europium, 98% of Cerium, 92% of Terbium and 89% of Lanthanum by leaching after soda ash roasting. In the leaching experiment with unroasted phosphor at 80 oC, the initial leaching reaction rate of Yttrium was 0.035 mol/L·s in 0.3N sulfuric acid solution, 0.033 mol/L·s in nitric acid solution and 0.028 mol/L·s in 0.3N hydrochloric acid solution. And the initial leaching reaction rate of Europium was 0.0017 mol/L·s in 0.3N sulfuric acid solution, 0.00114 mol/L·s in nitric acid solution and 0.00113 mol/L·s in 0.3N hydrochloric acid solution. For Cerium, the initial leaching reaction rate was 0.00019 mol/L·s in 0.3N sulfuric acid solution, 0.00025 mol/L·s in nitric acid solution and 0.00014 mol/L·s in 0.3N hydrochloric acid solution.

Radiocarbon Dating of Mortars and Charcoals from Novae Bath Complex: Sequential Dissolution of Historical and Experimental Mortar Samples with Pozzolanic Admixture

ABSTRACTCarbonaceous mortars from Novae (Bulgaria) contain local loess, crushed bricks and ceramic dust (pozzolanic materials). The reaction between lime and pozzolanic additives occurs easily and affects the rate and course of leaching reaction of carbonates in orthophosphoric acid during the sample pretreatment for dating. The composition of the Bulgarian mortars does not allow for unambiguous conclusions about chronology, but together with the observations of experimental mortars, gives new guidelines in terms of pozzolanic mortar application for dating. The presented research illustrates the possible reasons of difficulties with obtaining the appropriate portion of gas for radiocarbon (14C) measurement. To verify the relative chronology of legionary baths complex in Novae, the charcoals samples were also dated in addition to the mortar.

Study of the Process of Heavy Metals Cations Mineralization by Poly-Component Structures Based on Calcium and Magnesium Silicates

In order to achieve the goal of absorption of environmental pollutants, poly-component materials based on magnesium and calcium silicates - metal cations mineralizers – have been synthesized. The study of the processes of mineralization was carried out using model solutions containing soluble sulphates of copper, zinc, manganese and iron. The studies carried out have shown that the synthesized mineralizer based on calcium and magnesium silicates has a multicomponent structure with active electrochemically inhomogeneous centres on its surface as a result of breaking the Ca-O-Si, Mg-O-Si bonds, hydration and leaching of the Ca2+ and Mg2+ ions. In an acidic environment, the leaching reaction is activated due to H+ adsorption and the weakening of the bond between Ca2+ and O2-, thus making the transition of Ca2+ into the liquid phase more advantageous. As a result, a negatively charged ≡Si-O-layer enriched with silicon is formed, which is able to interact chemically with heavy metal ions present in the electrolyte solution.

Removal of Metal Impurities from the Spent Hydroprocessing Catalyst and Acid Leaching Kinetics of Aluminum

The impurity metal of Al in spent hydroprocessing catalyst (Mo-Ni/Al2O3) was removed by HCl, and the metals of Mo and Ni were preliminarily enriched. The results show that the leaching efficiency of Al was 88.62%, and the leaching efficiency of Mo and Ni were 16.32% and 28.74%, respectively. The results were achieved under optimal leaching conditions: the particle size was 150 μm, the concentration of HCl was 4 mol/L, the leaching temperature was 90 °C, and the leaching time was 120 min. The kinetics of the leaching behavior of Al showed that the acid leaching reaction of Al was in accorded with the equation 1-2/3X-(1-X) 2/3=K2t, R2=0.97734, which was controlled by internal diffusion. X-ray diffraction analysis of the leaching residue revealed the existence of residual metals Mo(MoO3, MoO2(ClO4)2)and Ni(NiS). The separation of Al from Mo and Ni has been preliminarily realized, which is conducive to further efficient recovery of Mo and Ni.

Chalcopyrite Leaching Kinetics in the Presence of Methanol

The dissolution of chalcopyrite under near ambient conditions represents one of the main challenges in the copper industry. Thus, various routes have been proposed for chalcopyrite treatment, such as the use of polar organic solvents, and this has shown promising results. In this paper, we present a study of copper leaching from a chalcopyrite concentrate in aqueous acidic medium with methanol and various H2O2 concentrations at 15, 30, and 40 °C. The results show that nearly complete copper extraction was attained within 5 h at 40 °C. The extraction percentages were plotted as functions of time at each temperature. The experimental data were modeled using the shrinking core model considering the cylindrical particle shape (shrinking cylinder model) within acceptable confidence levels, yielding an estimated activation energy of 24.3 kJ/mol. Furthermore, the process was dependent on the H2O2 concentration, and it acts as a reagent rather than an oxidant in the leaching reaction. It was found that sulfur is the only species present in the solid phase formed during the leaching of chalcopyrite, demonstrating the co-dissolution of both copper and iron.

Dissolution kinetics of Amazonian metakaolin in nitric acid

The kinetic study of Amazon metakaolin dissolution was performed with the application of the shrinking core model for spherical and ‘flat plate’ particles with constant size. The Amazon kaolin was calcinated at 700 ºC in order to produce metakaolin. This metakaolin was leached with 5% excess nitric acid at 70, 80 and 95±3 ºC for 3 h. Samples were collected every 15 min and subjected to aluminum analysis. The acid leaching was a chemically controlled process. The spherical morphology showed better fit than the flat plate particles when taking into account the regression coefficients. 91.58 kJ/mol of activation energy was found as well as an aluminum leaching reaction of the first order. The results found in this work using 5% excess acid and Amazon kaolin were consistent with previous research results using excess acid above 50% and standard kaolin.