Recovery of Gallium and Aluminum from Electrofilter Dust of Alumina Calcination Plant in Bayer Process

In this study, the recovery of gallium (Ga) and aluminum (Al) from the by-product of Bayer process, the electrofilter dust of a calcination plant, was studied. Factorial leaching tests were also designed based on the results of the preliminary tests. Effects of factors and their interactions on the extraction of Ga and Al were demonstrated using Analysis of Variance of the findings. In the factorial design, nitric acid (HNO₃) leaching tests up to 43.4% Ga and 35.2% Al were leached from the electrofilter dust. The addition of oxalic acid (H₂C₂O₄) significantly enhanced the sulphuric acid (H₂SO₄) leaching of the dust with up to 48.3% Ga and 39.6% Al extractions.     

Leaching kinetics of neodymium in sulfuric acid from E-scrap of NdFeB permanent magnet

The leaching kinetics of neodymium in NdFeB permanent magnet powder was analyzed for the purpose of recovery of neodymium in sulfuric acid (H₂SO₄) from E-scrap (electric scrap) of NdFeB permanent magnet powder treated by oxidation roasting to form a reactant. The reaction was conducted with H₂SO₄ concentrations ranging from 2.5 to 3.5M, a pulp density of 110.8 g/L, an agitation speed of 750 rpm, and a temperature range of 30 to 70 °C. After 4 h of leaching, the neodymium content in the E-scrap powders was completely converted into a neodymium sulfate (Nd₂(SO₄)₃) solution phase in H₂SO₄ in the condition of 70 °C and 3.0M H₂SO₄. Based on a shrinking core model with sphere shape, the leaching mechanism of neodymium was determined by the rate-determining step of the ash layer diffusion. Generally, the solubility of pure rare earth elements in H₂SO₄ is decreased with an increase in leaching temperatures. However, the leaching rate of the neodymium in E-scrap powders increased with the leaching temperatures in this study because the ash layer included in the E-scrap powder provided resistance against the leaching. Using the Arrhenius expression, the apparent activation energy values were determined to be 2.26 kJmol^?1 in 2.5M H₂SO₄ and 2.77 kJmol^?1 in 3.0 M H₂SO₄.     

Electrocatalysis of oxygen and hydrogen peroxide reduction by UPD of bismuth on poly- and mono-crystalline gold electrodes in acid solutions

The electrocatalytic effect of underpotential deposition (UPD) of bismuth on the cathodic reduction of oxygen and hydrogen peroxide has been investigated on poly- and mono-crystalline (111) and (100) gold electrodes in 0.5 M HClO₄ solution. On the bare gold substrates an incomplete 2-electron reduction of O₂ to H₂O₂ predominates, which in the presence of Bi³⁺ in the solution is positively catalysed indicated by a decrease of the overvoltage and an increase of the rate of H₂O₂ reduction. The catalytic effects can be correlated with the degree of Bi adsorbate coverage and the structural arrangement of Bi adatoms depending on the crystallographic orientation of the substrate. The effect of a mixed anion (Cl^?) and cation (Bi³⁺) adsorption on the reduction process was also studied.     

Stripping of Au(I) from a Loaded Cetyltrimethylammonium Bromide/Tributyl Phosphate Organic Solution: Conversion and Reduction

The recovery of Au(I) from cyanide leaching solutions by solvent extraction techniques has attracted wide interest in the past decades. However, no substantial progress in industries has been reported yet, because of the difficulties concerning gold stripping from loaded organic phases, such as the quaternary amines extraction systems. In this work, a new technique for the recovery of Au(CN)₂ ^? from the loaded cetyltrimethylammonium bromide / tributyl phosphate organic solution by a two‐step stripping procedure is suggested first by Au(CN)₂ ^? conversion by HCl into corresponding chloride complex ions, and then by chemical reduction of auro‐chloride complex ions in TBP organic phases to give metal gold powder. The influences of HCl concentrations, reaction time, and various reducing agents used on the percent gold conversion and reduction were investigated. About 33% of Au(CN)₂ ^? in the initial TBP organic phase could be precipitated as metal gold powder in the conversion step, while 67% was converted into AuCl₂ ^? or AuCl₄ ^? and held in the organic phase. Subsequently, the loaded organic phase after conversion was contacted with reducing agents such as sodium sulfite, ammonium oxalate, or hydrazine hydrate. Most (>98%) of the auro‐chloride complex ions could be effectively reduced as metal gold. As a result, the total gold recovery from the initial TBP organic phases after the two stripping procedures achieved more than 98%. The ¹⁹⁸Au radioactive tracer was employed to determine the concentration and distribution behavior of gold in both organic and aqueous solutions. In addition, the experiment on the reuse of the organic phase after gold stripping showed that there was no obvious loss in percent gold(I) recovery after one cycle of the extraction‐ stripping‐ regeneration process no matter what reducing agent was used.     

Selective Recovery of Cadmium,Cobalt, and Nickel from Spent Ni–Cd Batteries Using Adogen® 464 and Mesoporous Silica Derivatives

Spent Ni–Cd batteries are now considered an important source for many valuable metals. The recovery of cadmium, cobalt, and nickel from spent Ni–Cd Batteries has been performed in this study. The optimum leaching process was achieved using 20% H₂SO₄, solid/liquid (S/L) 1/5 at 80 °C for 6 h. The leaching efficiency of Fe, Cd, and Co was nearly 100%, whereas the leaching efficiency of Ni was 95%. The recovery of the concerned elements was attained using successive different separation techniques. Cd(II) ions were extracted by a solvent, namely, Adogen^® 464, and precipitated as CdS with 0.5% Na₂S solution at pH of 1.25 and room temperature. The extraction process corresponded to pseudo-2nd-order. The prepared PTU-MS silica was applied for adsorption of Co(II) ions from aqueous solution, while the desorption process was performed using 0.3 M H₂SO₄. Cobalt was precipitated at pH 9.0 as Co(OH)₂ using NH₄OH. The kinetic and thermodynamic parameters were also investigated. Nickel was directly precipitated at pH 8.25 using a 10% NaOH solution at ambient temperature. FTIR, SEM, and EDX confirm the structure of the products.     

Highly stable Fe/γ‐Al2O3 catalyst for catalytic wet peroxide oxidation

BACKGROUND: A highly stable Fe/γ‐Al₂O₃ catalyst for catalytic wet peroxide oxidation has been studied using phenol as target pollutant. The catalyst was prepared by incipient wetness impregnation of γ‐Al₂O₃ with an aqueous solution of Fe(NO₃)₃· 9H₂O. The influence of pH, temperature, catalyst and H₂O₂ doses, as well as the initial phenol concentration has been analyzed. RESULTS: The reaction temperature and initial pH significantly affect both phenol conversion and total organic carbon removal. Working at 50 °C, an initial pH of 3, 100 mg L^?1 of phenol, a dose of H₂O₂ corresponding to the stoichiometric amount and 1250 mg L^?1 of catalyst, complete phenol conversion and a total organic carbon removal efficiency close to 80% were achieved. When the initial phenol concentration was increased to 1500 mg L^?1, a decreased efficiency in total organic carbon removal was observed with increased leaching of iron that can be related to a higher concentration of oxalic acid, as by‐product from catalytic wet peroxide oxidation of phenol. CONCLUSION: A laboratory synthesized γ‐Al₂O₃ supported Fe has shown potential application in catalytic wet peroxide oxidation of phenolic wastewaters. The catalyst showed remarkable stability in long‐term continuous experiments with limited Fe leaching, < 3% of the initial loading. Copyright © 2010 Society of Chemical Industry     

A Model for The Recovery of Titanium From Mixtures of Ilmenite and Hematite by Hydrochloric Acid Leaching

Abstract

A partial equilibrium model has been developed to describe the leaching of FeTiO₃-Fe₉O mixtures by aqueous HC1. The model couples the rates of leaching of the minerals to changes in the solution species concentrations; 23 species concentrations were calculated as a function of leaching time. Solution reactions included in the model include (1) the redox reaction converting Ti(IV) and Fe(II) to Ti(III) and Fe(III); (2) formation of chloro complexes; (3) hydrolysis; and (4) dissociation of H₂O. Ilmenite is more rapidly depleted than hematite, and available data indicate that the time dependence of the leaching reactions is different. Modeling results show that the Ti/Fe concentration ratio drops steeply initially but then gradually rises as the leaching rates change. Of the two oxides, FeTiO₃ is consumed first, and thereafter the Ti/Fe ratio again declines. The Fe(II)/Fe(III) concentration ratio behaves similarly. The Ti/Fe and Fe(II)/Fe(III) ratios have simultaneous extrema and plots of these ratios vs. time can, with appropriate adjustments in vertical scale, virtually be superimposed. These changes are greatest when the initial molar amounts of FeTiO₃ and Fe₂O₃ are approximately equal. They are qualitatively the same, but of much smaller magnitude, when the initial FeTiO₃ /Fe₃O₃ molar ratio is far from 1.0. The species distributions change in a complex way during leaching; typically, hydroxo species become more important but chloro species become less so. Implications of these results for the selective recovery of titanium will be discussed.     

Optimization of gold recovery from copper anode slime by acidic ionic liquid

Hydrometallurgical gold recovery from primary or secondary sources is mainly based on a cyanide process, which is very dangerous for the environment due to the high toxicity levels. In view of the environmental effect, the present study proposes a new green solvent called 1-ethyl-3-methyl-imidazolium hydrogen sulfate (EmimHSO₄) ionic liquid (IL) to recover gold from copper anode slime (CAS). The optimum leaching conditions for maximizing gold recovery were determined by orthogonal array (OA) of Taguchi’s experimental design method. OA L₁₆ (4⁴) including four parameters with four levels each, was used to examine the effects of IL concentration (20%, 40%, 60%, 80% v/v), temperature (25, 50, 75, 95 °C), time (½, 1, 2, 4 h) and solid/liquid ratio (1/10, 1/15, 1/20, 1/25 g/mL) on leaching efficiency of the gold recovery. Statistical analysis of variance (ANOVA) was used to determine the relevance between experimental conditions and gold recovery. The selective leaching tests results showed that gold recovery up to 89.07% was attained on laboratory scale under the optimum leach conditions: 80% IL concentration, 75 °C, 4 h and 1/25 g/mL solid/liquid ratio. According to these results, EmimHSO₄ IL provides a very good ambiance for the oxidative leaching of gold and can be offered as an alternative leaching agent instead of harmful cyanide-based solvents.     

Decomposing the Titaniferous Magnetite Concentrate with Hydrochloric Acid

The decomposition of TMC with hydrochloric acid solutions (15–25% HCl) at the boiling point of the reaction mixture and atmospheric pressure has been investigated. The processing conditions have been determined for efficient recovery of titanium (up to 99.3%) as photocatalytically active anatase and for extracting Fe (up to 99.6%) and V (98.8%) into the leaching solution. Subsequent treatment of the leach liquor with aqueous ammonia affords 99.3 wt % Fe₂O₃ and an iron-vanadium product containing 3.2 wt % V₂O₅.     

Low‐temperature conversion of spent adsorbent to iodine sodalite by a mechanochemical route

The focus on a ball milling induced conversion as a possible synthesis route of iodine sodalite (Na₈Al₆Si₆O₂₄I₂) from zeolite‐based iodine adsorbents in order to treat a radioactive iodine filter for the off‐gas cleaning during nuclear facilities is presented. A mixture of silver iodide and zeolite 13X as a simulated adsorbent was mechanochemically milled using a laboratory‐scale planetary ball mill. The obtained powders were characterized by X‐ray diffraction to determine the effect of milling time on the conversion of the iodine sodalite. The crystal grain size and the lattice strain of the grounded phases were evaluated. After the ball milling, the milled samples were hydrothermally crystallized to form a sodalite phase with a sodium hydroxide solution for 48 h in an autoclave maintained at 150^°C. The iodine sodalite was successfully obtained after hydrothermal crystallization. A leaching test was carried out for the assessment of the order of iodine leachability and chemical durability under reducing conditions. The leaching amount was found to be low on the orders of 10^?4 ～10^?5 mol dm^?3 in sodium thiosulfate solution. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2441–2447, 2012     

Catalytic property of Fe-Al pillared clay for Fenton oxidation of phenol by H2O2

Clay pillared with Fe-Al was synthesized as a catalyst for Fenton oxidation of phenol by hydrogen peroxide (H₂O₂). The pillaring process altered the basal space of clay, which is related to the amounts of aluminium and iron in the pillaring solution. The catalytic activity of the pillared clay was attributed to the accessible iron species, whose amount is regulated not only by the introduced iron species but also by the basal space that subsequently depends on the introduced aluminium species. The heterogeneous Fenton reaction exhibited an induction period followed by an apparent first order oxidation of phenol by H₂O₂. The induction period was proposed as an activation process of the surface iron species, which is thus enabled to complex with the reactants. The induction time (t_I) depended on temperature (T) and pH condition but irrelevant to the concentrations of phenol and H₂O₂ and the amount of catalyst. The rate of the oxidation process was evaluated with respect to the concentrations of phenol and H₂O₂, the amount of catalyst, pH and temperatures. During the catalytic reaction the trend of iron leaching showed an ascending period and a descending period, which was related to the presence of ferrous ions and ferric ions. The Fe-Al pillared was recovered through two procedures, dry powder and slurry, which have different effect on the induction period.     

Co?N graphene encapsulated cobalt catalyst for H2O2 decomposition under acidic conditions

Hydrogen peroxide (H₂O₂) has been listed as one of the 100 most important chemicals in the world. However, huge amount of residual H₂O₂ is hard to timely decomposed into O₂ and H₂O under acidic condition, easily resulting in explosion hazard. Here, we reported a core–shell structure catalyst, that is graphene with Co N structure encapsulated Co nanoparticles. Co N graphene shell serves as the active site for the H₂O₂ decomposition, and Co core further enhance this decomposition. Benefiting from it, the H₂O₂ decomposition were close to 100% after 6 cycles without pH adjustment, which increased 6 orders of magnitude compared with no catalyst. At the same time, the O₂ generation reached 99.67% in 2 h with little metal leaching, and ·OH has been greatly inhibited to only 0.08%. This work can cleanly remove H₂O₂ with little deep oxidation and protect the process of H₂O₂ utilization to achieve a safer world.     

Characterization of nanoporous materials prepared from montmorillonite clay and its application to the decolorization of mare's milk oil

Nanoporous materials have been prepared by leaching the purified montmorillonite clay with sulfuric acid (H₂SO₄) solution with varying concentrations (0.5–2 M) at 80°C for 0.5–4 h. Acid leaching causes partial amorphisation of the clay with depletion of MgO, Al₂O₃, CaO and Fe₂O₃ components mostly from interlayer and octahedral sites. This increases the specific surface area by more than 3 times, i.e. from 49.1 to 157 m²/g. The pore-size distribution curves calculated from the adsorption isotherms of the leached montmorillonite show that most of the pores are in the mesoporous region with their diameter ranging 3–4 nm. This material turns out to be appropriate for bleaching of the mare's milk oil. The chemical and structural changes of the acid-leached montmorillonite are discussed in terms of the decolorization capacity.     

Solvent extraction of gold(I) from alkaline cyanide solution by dibutylcarbitol (DBC) with n‐octanol

BACKGROUND: Currently, cyanidisation is preferred for the extraction of gold because it has a number of advantages over other methods. Gold(I) can be extracted with various extractants, but there are no reports on the extraction of gold(I) from cyanide solution by dibutylcarbitol (DBC). In this work the extraction of gold(I) from alkaline cyanide solution using DBC with n‐octanol was studied. Several factors affecting the percentage extraction of gold(I), including DBC concentration, diluent concentration, equilibrium time, phase ratio, pH and gold concentration in aqueous phase, were investigated. RESULTS: The results showed that 96.2% of gold(I) could be extracted using an organic phase composed of 40% (v/v) DBC, 50% (v/v) n‐octanol and 10% (v/v) odourless kerosene. The extraction was quite fast and equilibrium could be established within 2 min. Stripping of the gold‐laden organic phase was carried out using sodium sulfite (Na₂SO₃) and sodium thiosulfate (Na₂S₂O₃) solutions, with Na₂S₂O₃ proving better than Na₂SO₃. The percentage stripping of gold(I) was 96.5% when the Na₂S₂O₃ concentration was 4% (w/w), and the stripping capacity of gold(I) exceeded 311.3 mg L^?1 when the phase ratio (A/O) was equal to 0.2. CONCLUSION: Gold(I) can be extracted from aqueous cyanide solution by DBC in the presence of n‐octanol and efficiently stripped by aqueous Na₂S₂O₃ solution. This method has the potential for practical application in the extraction and separation of gold. Copyright © 2008 Society of Chemical Industry     

IN SITU LEACHING OF URANIUM USING DILUTE SULFURIC ACID AND MOLECULAR OXYGEN

The technical feasibility of in situ uranium leaching using dilute sulfuric acid and molecular oxygen has been assessed and the important process parameters examined by use of laboratory high pressure leaching columns.

The dilute H₂SO₄/O₂ lixiviant was effective in leaching uranium from the ore samples tested. The leaching process was chemical reaction rate limited and can be represented using pseudo first-order kinetics. The leaching rate constant is proportional to the proton concentration of the lixiviant.

Much of the uranium was leached from the ore before decomposition of carbonate minerals by the acid was complete. Acid consumption per pound of U₃O₈ increased sharply as the uranium recovery level exceeded 70%. There appears to be a minimum oxygen pressure for effective uranium leaching. A pressure of 2758 KPa was adequate for the ore samples tested     

Heterogeneous fenton and photo‐fenton oxidation for paracetamol removal using iron containing ZSM‐5 zeolite as catalyst

Paracetamol is commonly found in wastewaters, as a consequence of its high consumption and incomplete elimination by conventional treatments. Homogenous (photo‐)Fenton oxidation has proved efficient for its remediation, but it suffers from uneasy dissolved iron recovery. Therefore this work examines the performance and stability of an iron containing zeolite (Fe/MFI) as catalyst for this reaction. Effects of reaction parameters (pH, temperature, catalyst and H₂O₂ concentrations, UV/vis irradiation) are investigated in batch conditions, by comparing the pollutant and Total Organic Carbon disappearance rates in solution, as well as the overall mineralization yield (including solid phase) and oxidant consumption. At near neutral pH paracetamol can be fully converted after 5 h, while TOC removal reaches up to 60%. Finally, thanks to good catalyst stability (low leaching), a continuous process coupling oxidation and membrane filtration is proposed, showing constant TOC conversion over 40 h and iron loss in the permeate <0.3 ppm. © 2016 American Institute of Chemical Engineers AIChE J, 63: 669–679, 2017     

Separation and recovery of copper from waste printed circuit boards leach solution using solvent extraction with Acorga M5640 as extractant

Waste printed circuit boards (WPCBs) have received extensive attention in recent years because of its harmfulness and resource. In this work, two-step leaching process was carried out by using steel pickling waste liquor (SPWL) as the leaching agent. The leaching solution contains a variety of metals, especially iron, which will have an effect on the recovery of copper. Acorga M5640 (M5640) extractant with a kerosene diluent was used to recover copper from WPCBs leach solution, and the separation factor is adopted to analyze the effects of these metal ions. The effect of different parameters such as pH of aqueous phase, phase ratio (O/A), M5640 concentration, contact time as well as the concentration of H₂SO₄ as stripping reagent were investigated. Over 90.0% copper was extracted with pH 1.1, phase ratio (O/A) 1/1, M5640 concentration 16%, contact time 3 min at room temperature. For the stripping process, the 60 s contact time and 2.5 mol/L H₂SO₄ concentration are suitable with 90.0% stripping percentage of copper. Copper extraction isotherm accords with Langmuir isotherm equation and the results show that iron is the most influential metal ion for copper extraction, which will reduce the theoretical saturation of the extractant. The extractant M5640 has excellent reuse performance and can be recycled more than 10 times, which demonstrated M5640 has the industrial application value in the extraction of copper from WPCBs leach solution.     

Leaching and electrochemical recovery of copper,lead and tin from scrap printed circuit boards

The recovery of copper, lead and tin from scrap printed circuit boards (PCBs) has been achieved using a combination of leaching, electrochemical ion exchange and electrodeposition. A simple aqueous nitric acid stripping solution, with the concentration range of 1–6 mol dm^?3, has demonstrated the potential for selective extraction of copper and lead from the PCBs. Precipitation of tin as H₂SnO₃ (metastannic acid) occurred at acid concentrations above 4 mol dm^?3. Preliminary galvanostatic electrolysis from simulated leaching solutions has investigated the feasibility of electrodeposition of copper and lead at different concentrations of HNO₃. Cathodic lead deposition, particularly at high electrolyte conditions, resulted in poor current efficiency. This was mainly due to dentritic metal formation and subsequent re‐dissolution. An alternative method investigated for recovering the metal values was the simultaneous electrodeposition of copper at the cathode and lead dioxide at the anode. Electrohydrolysis for acid and base regeneration from the spent nitric acid electrolyte has also been investigated. © 2002 Society of Chemical Industry     

Photoassisted hetero-Fenton mineralisation of azo dyes by Fe(II)-Al2O3 catalyst

Photoassisted Fenton mineralisation of two azo dyes Direct Red 23 (DR 23) and Reactive Orange 4 (RO 4) was studied in detail using a Fe(II) loaded Al₂O₃ as a heterogeneous catalyst in presence of H₂O₂ and UV-A light. 25 and 15% FeSO₄ loaded Al₂O₃ show the maximum efficiency in the degradation of DR 23 and RO 4 respectively. The effects of catalyst loading, H₂O₂ concentration, initial solution pH and initial dye concentration on photodegradation were investigated and the optimum conditions are reported. DR 23 undergoes easy degradation when compared to RO 4. The difference is due to the presence of stable triazine ring system in RO 4. The catalyst is reusable and the leaching of Fe(II) from the catalyst in each run is less than 10% in the pH range 2–7.