Leaching Percentage Research Articles

Kinetics Study on Microwave Alkaline Roasting-Water Dissolving of Germanium from Zinc Oxide Dust

Abstract Zinc hydrometallurgy plants produce large amounts of germanium (Ge)-containing zinc oxide (ZnO) dust during the production process. However, the present leaching percentages of Ge by the sulfuric leaching process from ZnO dust are generally lower than 60%. Thus, a novel process of microwave alkaline roasting followed by water dissolving is proposed to further improve Ge extraction from ZnO dust, and the kinetic behaviors and related theoretical models are studied. Perhaps it can be promoted Ge leaching percentages by water after microwave alkaline roasting, the dissolving reaction kinetics follow the diffusion control model, and the apparent activation energy is 15.46 kJ/mol.

Study on the Sulfuric-Leaching Kinetics of Germanium from Zinc Oxide Dust Assisted by Microwave Roasting

Abstract The Ge-bearing zinc oxide dust (ZnO) is commonly leached by sulfuric acid in industry, but the leaching percentage of Ge is only < 60%. To date, there is no suitable industrial process to address this problem. Thus, a novel process of microwave roasting followed by sulfuric acid leaching of Ge from ZnO dust is proposed to further improve Ge extraction from ZnO dust, and the kinetics behaviors and related theoretical models are studied. Results reveal that Ge leaching percentages are markedly increased by microwave roasting, the reaction kinetics follow the shrinking core model of the diffusion process of the solid film, and the apparent activation energy is 2.28 kJ/mol.

Hydrochloric acid leaching of rare earth elements from a novel source of deep-sea sediments and advantage of reduction with H2O2

In this study, the mineralogy of a novel resource of deep-sea sediments containing rare earth elements (REEs) was investigated, along with the leaching of REEs using hydrochloric acid. The results revealed that, apart from 62.0% of the Ce found in the Mn oxides, the other REEs in the deep-sea sediments mostly existed in hydroxyapatite mineral which can be easily decomposed via a hydrochloric acid leaching. An optimized REEs leaching percentage of 89.5% was achieved using 2.0 mol/L hydrochloric acid as the leaching agent, with a liquid-solid ratio of 4:1, at 60 °C for 30 min. However, Mn oxides remained stable during the leaching process, resulting in a low Ce leaching percentage of 30.7%. Under the optimized conditions, Mn oxides could be decomposed by adding 30% H2O2 as a reducing agent, leading to improved leaching percentages of Ce and REEs to 86.6% and 93.2%, respectively. The high leaching efficiency of REEs may further increase the utilization potential of this novel resource.

Solution circulation for green and sustainable gold extraction with an integrated low potential thiosulfate leaching-resin adsorption recovery process

A systematic research of solution circulation for gold extraction from a gold ore with an integrated low potential thiosulfate leaching-resin adsorption recovery process was performed by using the analysis and detection methods of ICP-OES, SEM-EDS, HPLC, XPS, etc. The pulp potential was controlled at about 200 mV under low reagent concentration and closed condition where the gold leaching percentage achieved 89.02 % while the thiosulfate consumption was only 19.22 kg/t. 100 % of the gold and 32.61 % of the copper in the leaching solution were adsorbed by the resin, and their desorption percentages separately reached 98.59 % and 98.86 % after selective two-stage desorption. The leaching and adsorption percentages of gold first decreased and separately kept at about 91 % and 96 % after 10 solution circulations while the gold desorption percentage and thiosulfate consumption were basically unchanged with solution circulation. The sulfur-oxygen anions in the solution including S2O32–, S3O62–, S4O62–, SO32– and SO42–, and only SO42– was gradually accumulated with solution circulation. SO42–, S2O32– and S3O62– were the main sulfur-oxygen anions adsorbed on the resin, and they did not accumulate obviously on the resin with solution circulation. The novelty of this study is that gold was recovered as elemental gold product based on the the proposed process, and the effect of solution circulation on gold extraction and the accumulation and conversion rules of sulfur-oxygen ions during solution circulation were revealed for the first time.

Thiocyanate facilitating thiosulfate extraction of gold via inhibiting formation of passive layer

Thiosulfate leaching is a feasible alternative for cyanidation. However, thiosulfate is easily decomposed and forms the passive layer on the ore surface, thus hindering gold extraction. In this paper, by adding thiocyanate to reduce the undesirable effect, copper-ammonia-thiosulfate leaching system is utilized to extract gold from the calcine. This research investigated the factors affecting gold extraction and kinetics of the leaching system, and the potential reason and reaction mechanism of the thiocyanate for improving gold leaching efficiency were discussed and analyzed. Gold leaching percentage is increased from 62.99% to 88.45% by adding thiocyanate that is close to that of cyanidation. By using X-ray photoelectron spectroscopy, gold in the leachate may be in the form of gold(I) thiosulfate complex. The leaching mechanism and the reason for improving gold extraction by adding thiocyanate were investigated via characterization and the leaching thermodynamic analysis. The possible reason for improving gold leaching percentage lied in that the thiocyanate reduced the decomposition of thiosulfate, thus inhibiting the form of passivation layer. According to the leaching mechanism, thiocyanate is used as an additive in the copper-ammonia-thiosulfate leaching system, which is of great significance for facilitating gold recovery, lessening thiosulfate consumption, and reducing ammonia dosage.

Do You Know What You Drink? Comparative Research on the Contents of Radioisotopes and Heavy Metals in Different Types of Tea from Various Parts of the World.

The aim of this study was to assess the potential health risks of radioactive elements and heavy metals ingested through the consumption of various types of tea imported to the Polish market (black, green, red, oolong and white). The concentrations [Bq/kg] of radionuclides (40K, 137Cs, 226Ra, 210Pb and 228Th) in tea leaves before and after brewing were measured using γ-ray spectrometry with high-purity germanium (HPGe). The concentrations [mg/kg] of the studied elements (Fe, Cr, Cu, Mo, Al, Mn, Ni, P, V, Cd and Pb) were determined using a microwave-induced plasma optical emission spectrometer (MIP-OES). The results presented here will help to expand the database of heavy metals and radioactivity in teas. With regard to the potential health risk, the percentage of leaching of individual elements in different types of tea infusions was determined, and the assessment of the consumption risk was estimated. Since the calculated exposure factors, namely the HQ (Hazard Quotient) and THQ (Target Hazard Quotient), do not exceed critical levels, teas can still be considered health-beneficial products (most of the radionuclides as well as elements remain in the leaves (65-80%) after brewing).

Arsenic removal from coal by ferric chloride enhanced leaching under ultraviolet irradiation during flue gas desulphurization with coal slurry

ABSTRACT During coal combustion, the harmful element arsenic can be released into environment and cause potential significant harm to human beings. Therefore, it is very important to study the removal of arsenic from coal before combustion. In this work, simulated SO2-containing flue gas was used to leach arsenic from coal in a 1 L UV photoreactor. The effects of FeCl3, ultraviolet (UV), pH and the Cl−/Fe3+ molar ratio on arsenic leaching and SO2 removal were experimentally investigated and the enhancing mechanism was analysed. Experimental results demonstrated that FeCl3 and UV could efficiently increase iron and arsenic leaching percentages and SO2 removal efficiency. UV irradiation could induce the oxidation of most trivalent arsenic. The arsenic leaching percentage was significantly larger than that of iron. Low pH was favourable for iron and arsenic leaching. The optimal Cl−/Fe3+ molar ratio was determined to be 3:1. The introduced ferric chloride could not only increase the concentrations of free radicals and ferric iron oxidants, the chloride ion might also impede the formation of passive coatings, thus increasing the arsenic leaching percentage, intensifying the oxidation of trivalent arsenic and enhancing the removal of SO2.

Gold Leaching from Printed Circuit Boards Using a Novel Synergistic Effect of Glycine and Thiosulfate

Printed circuit boards (PCBs) are a secondary source for the extraction of precious metals, such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd), etc. Thiosulfate and glycine systems have recently gained a significant amount of attention for Au leaching. However, in the thiosulfate system, the stability of leached Au tends to decrease when using lower thiosulfate concentrations. In this study, a copper–ammonia–thiosulfate system (thiosulfate system) and glycine or histidine were combined to leach Au from PCBs. The glycine–thiosulfate system resulted in a higher Au leaching than the histidine–thiosulfate system. The results revealed that the glycine–thiosulfate system exhibited a synergistic effect on Au leaching (93.7%) at pH 9.3 and 40 °C, while the Au leaching percentages were 47.1% and 50.7% for the thiosulfate and glycine systems, respectively. In the dual system, Fe leaching was insignificant, although Ag and Al leaching were 95.3% and 27.0%, respectively. Compared to the thiosulfate system, the dual system maintained the stability of the leached Au. The system required 60 mM thiosulfate and 0.5 M glycine at 40 °C and pH 9.3 in order to leach Au from PCBs. The kinetic study suggested that Au and Ag leaching from PCBs in the dual system followed the diffusion-controlled model. The Au leaching rate in the initial phase of the dual system was similar to that of the glycine–cyanide system. This novel, mild approach could be applied to hydrometallurgy to leach other precious metals from sources, such as ore and spent catalysts.

The structure evolution of halloysite nanotubes during the acid leaching process: A molecular dynamics study

For the acid-leaching process of halloysite nanotubes (HNTs), the structure and energetic evolution is crucial for the basic understanding and further modification of HNTs. The specific surface area, pore volume, and bond distribution of HNTs at different Al leaching percentages were studied by molecular dynamics simulation. With the increase of the Al leaching percentage, the inner diameter of the halloysite nanotubes is gradually enlarged, forming some nanoporous (1–20 nm) interlayer spaces inside the tube wall of HNTs due to the strong bondings between the adjacent layers, and the specific surface area and pore volume of HNTs increased in a complex way at each transition stages. For the transition structures, the interlayer nanopores greatly increase the specific surface area and pore volume of HNTs, which is more obvious after 50% Al leaching. The free water molecules inside lumen structure of HNTs would have an impact on the thermodynamics and the structure evolution of HNTs. Although the transition structures with extremely large loading capacity may not be naturally most stable, they might be stabilized or achieved by some fast transient regulation methods.

Exploring key physicochemical sediment properties influencing bioleaching of heavy metals

Bioleaching is a promising technology to remediate sediments contaminated by heavy metals. However, the complex heterogeneities of the sediments can reduce the acidification efficiency and the heavy metal removal rate, thus hindering the practical application of sediment bioleaching. This experiment conducted comparative bioleaching experiments between the inoculated group (average leaching percentages: Cu 67.64%; Zn 54.44%; Ni 29.59%) and the non-inoculated control group (Cu 37.10%; Zn 41.04%; Ni 19.89%) on 28 sediments characterized by different physicochemical properties to explore the key factors influencing bioleaching. The results indicated that the bioleaching process was predominated by the indigenous bioleaching bacteria and the bioleaching inoculum, respectively. The ACCpH=4 (acid-consuming capacity), TOC (total organic carbon), and TN (total nitrogen) of the sediments played an essential role in influencing the microbial community structure and bioleaching performance: the ACCpH=4, as the inhibitive factor, could influence the succession growth of the indigenous bioleaching bacteria and the inoculum during the bioleaching process, while the TOC and TN, as the contributing factor, could influence the metabolism of the indigenous bioleaching bacteria. Based on these results, the bioleaching process was improved with the classification and pretreatments of sediment to realize successful bioleaching of all types of the sediments examined in this research.

Gold extraction using alternatives to cyanide: Ultrasonic reinforcement and its leaching kinetics

A novel eco-friendly synthetic gold lixiviant (Jinchan) was used to recover gold from gold ores. Ultrasound was used to improve gold leaching efficiency and recovery percentage. The differences between ultrasonic and conventional leaching were investigated by comparing the effects of temperature, ultrasonic power, pH variation, and Jinchan concentration on gold leaching. The gold leaching percentage could be effectively increased from 42.21 % to 94.72 % using ultrasound, and the gold leaching time could be reduced. Kinetic studies indicated that Jinchan leaching was primarily controlled by internal diffusion. The apparent activation energy could be effectively reduced from 30.12 kJ/mol to 23.07 kJ/mol under ultrasound reinforcement. The reaction rate constant (k) of leaching was significantly improved by ultrasound.

Photo-assisted bismuth ferrite/manganese dioxide/nickel foam composites activating PMS for degradation of enrofloxacin in water

In order to further expand the practical applicability of nano photo-activators, a low-toxicity bismuth ferrite mixture (BFO) combined with MnO2 were used to construct nano-catalyst@nickel foam (NF) composite material. A variety of characterization methods were applied to determine the physical, chemical and photoelectrochemical properties of BFO/MnO2@NF. Subsequently, the performance of BFO/MnO2@NF/PMS/Light degradation system was evaluated through the enrofloxacin (ENR) removal experiment. And 87.5% of ENR could achieve removal with 4 cm2 of BFO/MnO2(3:1)@NF and 0.6 g L−1 of peroxymonosulfate (PMS) at the pH of 6.86 in the coupled system. In addition, during the ENR degradation process, the leaching percentages of Bi, Fe, and Mn ions in the BFO/MnO2 nano powder and BFO/MnO2@ NF were 0.041%, 0.29%, 0.12% and 0.035%, 0.068%, 0.084% (0.035% of Ni dissolution), respectively. It could be seen that the leaching concentration of metal ions during the reaction of the nickel foam-supported composite material was much lower than that of the corresponding nano-catalysts powder. Furthermore, the coupled system maintained excellent catalytic performance even after 8 running cycles. Thus, the BFO/MnO2@NF was easy to recover from the system and met the needs of practical applications, which would provide more opportunities for the design of nano-catalysts and practical applications in wastewater treatment processes.

Kinetics Investigation of Phosphorus Leaching from Steelmaking Slag

ABSTRACT The removal of phosphorus is essential to recycling steelmaking slag in metallurgical processes. In this study, dilute nitric acid was selected as the leaching agent for dissolving steelmaking slag. The effects of the variables on leaching percentage of phosphorus were investigated. Experimental results showed that, the leaching percentages of phosphorus increase as the concentration of nitric acid increases. Increasing the liquid/solid ratio and decreasing the slag particle size increased the leaching percentages of the phosphorus. However, the temperature and stirring speed had minor effects on the dissolution of phosphorus. Diffusion through the product layer was the rate-limiting step of the leaching process, and the corresponding apparent activation energy was determined to be 1.61 kJ/mol. Based on experimental results, a semi-empirical kinetic equation was established.

Recovery of Rare Metals from Superalloy Scraps by an Ultrasonic Leaching Method with a Two-Stage Separation Process

Superalloy scraps are deemed as potential unconventional sources of rare metals. In this study, an ultrasonic leaching method with a two-stage separation process was proposed. A series of Eh-pH diagrams for rare metals was constructed, and the results indicated that the leaching and separation process could be realized by adjusting the potential and pH values of leaching solutions. In the ultrasonic leaching process, results showed that the economic leaching percentages of Re, Ni, Co, Al, and Cr were 92.3%, 95.2%, 98.5%, 98.7%, and 97.5%, respectively. Compared with conventional leaching, ultrasonic leaching can improve the leaching percentages of rare metals by approximately 20%. In the two-stage separation process, the optimal recovery efficiencies of Al and Cr were 94.6% and 82.1% at a pH of 4.5, and Ni and Co were 99.5% and 98.3% at a pH of 7.5. With a two-stage precipitate process, rare metals can be efficiently recovered without generating any waste acid.

Development of in-situ electro-generated chlorine leaching and its application to the leaching of platinum

ABSTRACT An in-situ electro-generated chlorine leaching with a closed recycling unit of unconsumed gas was developed for precious metal dissolution and applied to the leaching of platinum from a spent automotive catalyst containing 0.13 wt% Pt. Cathodic current in a cathodic compartment of the chlorine generation cell reduces the unconsumed chlorine gas into chloride ions for further chlorine generation. The electro-reduction efficiency was 99.4% in alkaline 2 M NaCl solution, whereas 80.8% in 35% HCl solution at 0.62 mmol min−1 supply rate of unconsumed chlorine gas. The 98.3% platinum from the spent automotive catalyst leached without discharging the unconsumed chlorine gas into the air at 100 g L−1 solid/liquid ratio and 80°C in a 7 M HCl solution. Increasing the solid/liquid ratio to 400 g L−1 drastically decreased the leaching percentage to 16.5% in 90 minutes by possible adsorption of leached Pt to the porous surface of the automotive catalyst carrier.

Mechanism of synergistic pretreatment with ultrasound and ozone to improve gold and silver leaching percentage

Refractory gold ore is becoming the main gold resources at present. The sulfide coating on the surface of gold inhibits the leaching of gold and increases the consumption of reagents. The synergistic pretreatment ofozone and ultrasound is utilized to oxidize the sulfide coatings on the surface of gold and the synergistic mechanism is studied. Theozone and ultrasound pretreatment prominently increased the leaching percentage of gold from 49.12% to 93.52% and the leaching percentage of silver from 4.01% to 61.25% after 4 h. During the pretreatment, ozone effectively oxidized the sulfide enclosure(FeS2). The secondary-enclosure caused by pyrite oxidation is significantly inhibited by ultrasound. Meanwhile, the ultrasound significantly reduces particle size and increases specific surface area of the refractory gold ore, which intensified the oxidation process during the pretreatment. The pretreatment of ultrasound and ozone not only oxidized pyrite enclosure, effectively damaged pyrite enclosure and restrain secondary enclosure within a short time, also evidently increased the gold and silver leaching percentage.

A systematic and comparative study of copper, nickel and cobalt-ammonia catalyzed thiosulfate processes for eco-friendly and efficient gold extraction from an oxide gold concentrate

A systematic and comparative research was performed using copper, nickel and cobalt-ammonia catalyzed thiosulfate processes for environmentally friendly and efficient gold extraction from an oxide gold concentrate. 88.3% of gold was leached by thiosulfate with conventional copper-ammonia catalysis while its thiosulfate consumption was as high as 53.6 kg/t-concentrate. Thiosulfate consumption was reduced to 26.5 and 30.6 kg/t-concentrate, and 81.2% and 90.2% of gold leaching percentages were obtained with nickel-ammonia and cobalt-ammonia catalyses. The electrochemical leaching mechanism combined with XPS and SEM-EDS analyses illustrated the essential reason for the differences of three catalyses in gold leaching percentage and thiosulfate consumption. For copper-ammonia catalysis, two-stage desorption was required to desorb gold from the gold-loaded resin due to the co-adsorption of copper with gold while one-stage desorption was feasible for nickel-ammonia and cobalt-ammonia catalyses because nickel and cobalt did not co-adsorb with gold, and their gold recovery percentages were 82.4%, 98.5%, 97.7%, respectively. After 6-time cycles of barren leachate, the gold leaching and recovery percentages of copper-ammonia catalysis considerably decreased while those of nickel-ammonia and cobalt-ammonia catalyses only declined slightly. Thiosulfate leaching with cobalt-ammonia catalysis has the advantages of high gold leaching percentage, low thiosulfate consumption, simple desorption process, good leachate stability and recycle performance of barren leachate, and therefore it has a bright industrial application prospect.

Vibrational Spectral Analysis of Natisite (Na2TiSiO5) and its Structure Evolution in Water and Sulfuric Acid Solutions.

Natisite (Na2TiSiO5) is a layered sodium titanosilicate containing TiO5 square pyramids. The structure evolution of natisite in water and acid solutions is the basis for its potential applications. With Na2SiO3 as the silicon source, natisite with the shape of the square sheet was selectively prepared from the hydrothermal method with 14.3 mol/L NaOH solution at 240 °C. Natisite has 20 Raman active modes and 22 infrared active modes from the first-principles calculations within density functional theory, and the calculated Raman and infrared spectra agree well with the experimental ones. The characteristic Raman peak at 844 cm−1 is caused by the symmetric stretching of the apical Ti–O bond in the TiO5 unit, assigning to A1g and B2g modes. Natisite remains relatively stable in water with a sodium leaching percentage of lower than 6%. When washing with sulfuric acid solutions, the interlayer spacing of natisite is reduced due to the extensive removal of sodium ions, and an intermediate composed of SiO4 and newly formed TiO6 units may be formed. Moreover, after washing with water and acid solutions, 95.5%, 63.4%, and 35.2% of Na, Si, and Ti in natisite can be leached in total, respectively, resulting in the structural disintegration of natisite.

Use of dry grinding process to increase the leaching of gold from a roasted concentrate containing hematite in the thiosulfate system

Iron-containing oxides are the main minerals associated with roasted gold concentrates. The influence of different iron-containing oxides on the gold thiosulfate leaching process is very complex. In this study, we found the use of dry grinding methods can considerably eliminate the adverse effects on gold thiosulfate leaching under wet grinding conditions for a roasted gold concentrate containing hematite. The leaching results of gold ore showed that the gold leaching percentage was significantly improved from only 35% in 8 h under wet grinding conditions to 85% under dry grinding conditions. Using dry grinding to replace wet grinding, the loss of copper ions in the solution is much lower, and the diffusion coefficient of copper ions in the slurry is higher. Scanning electron microscopy (SEM) characterization shows that the passivation of the gold surface is much reduced. X-ray photoelectron spectroscopy (XPS) detection shows that the material adsorbed on the gold surface is mainly FeOOH. In addition, X-Ray diffraction (XRD) analysis results indicate that under wet grinding conditions, part of the hematite is transformed into goethite. Combined with the leaching results of gold powder, it is confirmed that the formed goethite during wet grinding is the cause of the deterioration of the gold leaching. Dry grinding can effectively avoid the formation of goethite and thus is a useful method to increase the gold leaching rate.

Effect of Si/Al molar ratio on the immobilization of selenium and arsenic oxyanions in geopolymer.

The effect of Si/Al molar ratio of geopolymer on the immobilization of Se and As oxyanions was studied through leaching test and solid characterizations including XRD, FTIR, TG, NMR, XAFS, and N2 adsorption-desorption isotherm. As a whole, the leaching percentages of Se and As oxyanions increased with the increase of the Si/Al molar ratio of geopolymer. Linear combination fitting confirmed that most of selenite, selenate and arsenate ions existed in geopolymers through electrostatic interaction. Thus, Al tetrahedrons in geopolymer structure control the charge stability for these oxyanions to a large extent. Differently, as for arsenate ions, they were recrystallized into an arsenate compound (Na3.25(OH)0.25(H2O)12)(AsO4) in geopolymers. The additive of these pollutants has an adverse effect on the compactness of geopolymer, then influencing the leaching performance in turn. However, the changes in leaching results did not follow the variation trend of specific surface areas and pore volumes of geopolymers with different Si/Al ratios. The number and distribution of Al tetrahedron and compactness of geopolymer have a synergistic effect on the immobilization of these oxyanions. Besides, the compressive strengths of geopolymer samples are always higher than 20MPa, which meets the requirement of safe disposal of hazardous waste.