Recovery of carbon and cryolite from spent pot lining of aluminium reduction cells by chemical leaching

A two-step alkaline-acidic leaching process was conducted to separate the cryolite from spent pot lining and to purify the carbon. The influencing factors of temperature, time, and the ratio of liquid to solid in alkaline and acidic leaching were investigated. The results show that the recovery of soluble compounds of Na3AlF6 and Al2O3 dissolving into the solution during the NaOH leaching is 65.0%,and the purity of carbon reaches 72.7%. During the next step of HCl leaching, the recovery of soluble compounds of CaF2 and NaAl11O17 dissolving into the HCl solution is 96.2%, and the carbon purity increases to 96.4%. By mixing the acidic leaching solution and the alkaline leaching solution, the cryolite precipitates under a suitable conditions of pH value 9 at 70 °C for 2 h. The cryolite precipitating rate is 95.6%, and the purity of Na3AlF6 obtained is 96.4%.

Behaviours of REE and Other Trace Elements During Pedological Weathering-Evidence from Chemical Leaching of Loess and Palaeosol from the Luochuan Section in Central China

The chemical leaching method is used for a systematic analysis of distribution characteristics of acid-soluble and acid-insoluble REE and other trace elements from the Luochuan loess deposits. The study shows that the acid-insoluble phase in loess and palaeosol is a stable component of old aeolian dusts and is characteristic of the provenance; the acid-soluble phase is the unstable component in the weathering pedogenic process and reflects rock-forming features after accumulation of aeolian dusts. The acid-insoluble REE and acid-soluble Sr and Pb can be used as geochemical indicators respectively to trace the provenance characteristics and the weathering pedogenic process.

Chemical leaching mechanism of chalcopyrite with difference mineralization

This paper presents the effect of mineralization on chalcopyrite chemical leaching in very simple H2SO4 solution systems at pH 1.0, with 5 % chalcopyrite con- centrate at 65 ~C. The copper extractions after 12 days leaching of marine volcanic and porphyry chalcopyrite were 85.7 and 66.6 %, respectively. It was found that sulphur element formed on the surface of two samples as a result of XRD and SEM-EDAX, which was very porous that did not inhibit chemical leaching reaction. Meanwhile, （Cu, Fe）12As4S13 formed on the surface of porphyry type chalcopyrite, which may cause low leaching ratio of por- phyry type chalcopyrite as passivation. （Cu, Fe）12As4S13 may be one kind of the polysulphide compounds.

Effect of moderately thermophilic bacteria on metal extraction and electrochemical characteristics for zinc smelting slag in bioleaching system

The effects of moderately thermophilic bacteria on the extraction of metals from zinc smelting slag and electrochemical characteristics of zinc smelting slag carbon paste electrode in bioleaching process were studied. The results show that the extraction rates of Fe, Cu and Zn from the slag reach 86.7%, 90.3% and 66.7% after adsorbed bacteria sterilize, while those with adsorbed bacteria are 91.9%, 96.0% and 84.5% in conditions of pulp density 2%, pH 1.0, temperature 65 °C and stirring rate 120 r/min, respectively. Some stretching peaks of functional groups from bacterial secretes on the bioleached residue surface, such as 1007 cm-1 and 1193 cm-1, turn up through FI-IR analysis and indirectly reveal the presence of the adsorbed bacteria on the slag particles surface. Besides, the corrosion of zinc smelting slag is enhanced by bacteria according to the characteristics of cyclic voltametry and Tafel curves in bioleaching system.

pH-dependent leaching mechanism of carbonatitic chalcopyrite in ferric sulfate solution

The dissolution of a carbonatitic chalcopyrite(CuFeS2)was studied in H_(2)SO_(4)−Fe_(2)(SO_(4))_(3)−FeSO_(4)−H_(2)O at varying pH values(0.5−2.5)and 25℃ for 12 h.Experiments were conducted with a size fraction of 53−75μm.Low Cu recoveries,below 15%,were observed in all pH regimes.The results from the XRD,SEM−EDS,and optical microscopic(OM)analyses of the residues indicated that the dissolution proceeded through the formation of transient phases.Cu_(3.39)Fe_(0.61)S_(4) and Cu_(2)S were the intermediate phases at pH 0.5 and 1.0,respectively,whereas Cu_(5)FeS_(4) was the major mineral at pH 1.5 and 1.8.The thermodynamic modelling predicted the sequential formation of CuFeS_(2)→Cu_(5)FeS_(4)→Cu_(2)S→CuS.The soluble intermediates were Cu_(5)FeS_(4) and Cu2S,whilst,CuS and Cu_(3.39)Fe_(0.61)S_(4) were the refractory phases,supporting their cumulating behaviour throughout the dissolution.The obtained results suggest that the formation of CuS and Cu_(3.39)Fe_(0.61)S_(4) could contribute to the passive film formed during CuFeS_(2) leaching.

Treatment of fir wood with chitosan and polyethylene glycol

Chitosan is a natural biopolymer, derived from chitin, which is used for wood modification. Polyethylene glycol（PEG） was reacted with wood to provide possible fixation of the chitosan to wood. Wood blocks were treated with chitosan and PEG, as well as pre-treatment with the PEG at different temperatures and further reaction with the chitosan. The samples were soaked in water to study leaching of the chemicals, water absorption, swelling, as well as anti-swelling efficiency. Any prior reaction of the wood with PEG provided better reaction to the chitosan.Bulking was increased after the treatment of the wood with PEG. Swelling was reduced in the PEG-treated wood blocks as well as the pre-treated samples. Chitosan was not able to protect wood against water penetration： the treated samples showed more water absorption and swelling.However, pre-treatment of the samples decreased swelling in the wood, and the density was not noticeably affected by the treatments. Heating during the treatment caused more reduction in swelling for PEG–chitosan treated samples.

Biodegradable Behavior of Waste Wool and Their Recycled Polyester Preforms in Aqueous and Soil Conditions

Present study deals with the biodegradable behavior of individual components and their preforms of nonwoven biocomposites developed from waste wool fibers including coring wool(CW),dorper wool(DW)and recycled polyester fibers(RPET).A respirometric technique was employed to estimate the production of CO_(2) during the biodegradation experiments under soil and aqueous media conditions.Functional groups of test samples before and after biodegradation were analyzed using Fourier transform infrared spectroscopy(FTIR).Leaching chemicals such as formaldehyde(hydrolyzed)and Chromium VI(Cr VI)was also measured.The CO_(2) emission in wool fibers CW and DW indicated 90%and 60%biodegradation in soil burial and aqueous media conditions respectively,for 100 days incubation.RPET fibers,20%and 10%biodegradation in soil burial and aqueous media conditions was measured respectively while the preforms of waste wool and RPET reflected 30%and 25%biodegradation in soil burial and aqueous media conditions,respectively.The degradation of end functional groups such as carbonyl(keto and ester),aldehyde and hydroxyl were also confirmed by FTIR.The DW and CW wool fibers showed higher Cr(VI)concentration as compared to the RPET.The released formaldehyde results showed higher concentration for RPET preforms as compared to waste wool preforms.These results suggest that waste wool preforms are extremely environment friendly as compared to RPET preforms.Thus,waste wool preforms it can be potentially utilized for preparing biocomposite materials and associated biobased products.

从废旧电池中直接提取锂实现锂的高效回收

The flourishing expansion of the lithium-ion batteries(LIBs) market has led to a surge in the demand for lithium resources. Developing efficient recycling technologies for imminent large-scale retired LIBs can significantly facilitate the sustainable utilization of lithium resources. Here, we successfully extract active lithium from spent LIBs through a simple, efficient, and low-energy-consumption chemical leaching process at room temperature, using a solution comprised of polycyclic aromatic hydrocarbons and ether solvents. The mechanism of lithium extraction is elucidated by clarifying the relationship between the redox potential and extraction efficiency. More importantly, the reclaimed active lithium is directly employed to fabricate LiFePO_(4) cathode with performance comparable to commercial materials. When implemented in 56 Ah prismatic cells, the cells deliver stable cycling properties with a capacity retention of ~90% after 1200 cycles. Compared with the other strategies, this technical approach shows superior economic benefits and practical promise. It is anticipated that this method may redefine the recycling paradigm for retired LIBs and drive the sustainable development of industries.

Low-cost adsorbents for urban stormwater pollution control

Stormwater represents a major non-point pollution source at an urban environment.To improve the treatment efficacy ofstormwater infrastructure,low-cost adsorbents have increasingly gained attention over the past decades.This article aims to briefly discuss several key aspects and principles for utilization of low-cost adsorbents for urban stormwater treatment.To determine whether a low-cost adsorbent is suitable for stormwater treatment,two aspects should be carefully assessed,including:1)its adsorption mechanisms and behaviors that can influence the binding strength,adsorption kinetics,and treatment capacity;and 2)unwanted chemical leaching patterns that can affect the extent of water quality degradation.Furthermore,the application mode of an adsorbent in the system design influences the utilization efficiency.Adsorbents,after dosed to soil media in infrastructure,would eventually become ineffective after oversaturation.In contrast,standalone filters or innovative composite adsorbents(e.g.,adsorbent-coated mulch chips)can enable a long-lasting adsorption due to periodic replacement with fresh adsorbents.The aforementioned principles play a key role in the success of urban stormwater treatment with low-cost adsorbents.