Hydrometallurgical detoxification and recycling of electric arc furnace dust

Electric arc furnace dust(EAFD)is a hazardous waste but can also be a potential secondary resource for valuable metals,such as Zn and Fe.Given the increased awareness of carbon emission reduction,energy conservation,and environmental protection,hydrometallurgical technologies for the detoxification and resource use of EAFD have been developing rapidly.This work summarizes the generation mechanisms,compositions,and characteristics of EAFD and presents a critical review of various hydrometallurgical treatment methods for EAFD,e.g.,acid leaching,alkaline leaching,salt leaching,and pretreatment–enhanced leaching methods.Simultaneously,the phase transformation mechanisms of zinc-containing components in acid and alkali solutions and pretreatment processes are expounded.Finally,two novel combined methods,i.e.,oxygen pressure sulfuric acid leaching combined with composite catalyst preparation,and synergistic roasting of EAFD and municipal solid waste incineration fly ash combined with alkaline leaching,are proposed,which can provide future development directions to completely recycling EAFD by recovering valuable metals and using zinc residue.

Application of a Sulfur Removal Hydrometallurgical Process in a Lead-Acid Battery Recycling Plant in Costa Rica

This study presents the implementation of a desulphurization process for lead recycling under different chemical and physical conditions using pyro-metallurgical processes. Desulphurization was done using a hydrometallurgical process using sodium carbonate as a desulphurization agent and different lead-bearing loads compositions. Waste characterization included: SO2 concentrations in the stack emissions, total lead content in the furnace ash, the total lead content in the slag, and the toxicity characteristic leaching procedure (TCLP). A significant reduction in SO2 emissions was achieved (~55% reduction) where mean SO2 concentrations changed from 2193 ± 135 ppm to 1006 ± 62 ppm after the implementation of the modified processes. The desulfurized lead paste (i.e. the metallic fraction lead of the battery) of the modified process exhibited an improvement in the concentration of the lead in the TCLP test, with an average value of 1.5 ppm which is below US EPA limit of 5 ppm. The traditional process TCLP mean value for the TCLP was 54.2 ppm. The total lead content in the bag house ashes shows not significant variations, when comparing the desulphurization (67.6% m/m) and non-desulphurization process (64.9% m/m). The total lead mean content in the slag was higher in the desulphurization process (2.49% m/m) than the traditional process (1.91% m/m). Overall, the implementation of a new desulphurization method would potentially increase the operation costs in 10.3%. At the light of these results, a combination of hydrometallurgical and pyro-metallurgical processes in the recycling of lead-acid batteries can be used to reduce the environmental impact of these industries but would increase the operational costs of small lead recyclers.

Recycling of spent lithium-ion batteries as a sustainable solution to obtain raw materials for different applications

Lithium-ion batteries(LIBs)containing graphite as anode material and LiCoO_(2),LiMn_(2)O_(4),and LiNi_(x)Mn_(y)Co_(z)O_(2) as cathode materials are the most used worldwide because of their high energy density,capacitance,durability,and safety.However,such widespread use implies the generation of large amounts of electronic waste.It is estimated that more than 11 million ton of LIBs waste will have been generated by 2030.Battery recycling can contribute to minimizing environmental contamination and reducing production costs through the recovery of high-value raw materials such as lithium,cobalt,and nickel.The most common processes used to recycle spent LIBs are pyrometallurgical,biometallurgical,and hydrometallurgical.Given the current scenario,it is necessary to develop environmentally friendly methods to recycle batteries and synthesize materials with multiple technological applications.This study presents a review of industrial and laboratory processes for recycling spent LIBs and producing materials that can be used in new batteries,energy storage devices,electrochemical sensors,and photocatalytic reactions.

AN EXPERT CONTROL SYSTEM FORPURIFICATION PROCESS

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Cobalt Recovery from Waste Catalysts (Petroleum Refining Industry from Gujarat)

A hydrometallurgical process has been developed for cobalt recovery from a waste catalyst (petroleum refining industry). This waste catalyst containing about 2.18 weight % of Co, is highly contaminated by Mg, Al, Si, Ca, Fe, Ni, Cu, Zn, Mo. The major steps are: (I) The spent catalyst is roasted with flux material in an electrical furnace at very high temperature (700?C) for a specific duration. (II) The roasted sample is leached with sulphuric acid to bring the metal contents into solution form. (III) For separating cobalt values from the leach solution, the solution pH is raised by NaOH addition, where all cobalt content is precipitated at a pH of about 12. (IV) This cobalt hydroxide precipitate is filtered and dissolved in minimum amount of sulphuric acid to get cobalt sulphate solution which is used as the electrolyte for the electrolytic recovery of cobalt. For optimizing various parameters like (1) H2SO4 concentration;(2) Duration;(3) Cobalt concentration;(4) Current density;(5) Temperature;(6) Stirring etc., The particle surface morphology and deposited layers have been characterized by scanning electron microscopy (SEM). A compact metallic deposit containing 70% cobalt was obtained.

Hydrometallurgy two stage process for preparation of (Nd,La,Ce)_(2)O_(3) from end-of-life NiMH batteries

The present work aims to investigate the recovery of light rare earth elements(LREEs) oxides from end-oflife NiMH batteries using a hydro metallurgical process followed by effective precipitation.The operational leaching parameters such as phosphoric acid concentration,temperature,and the solid-liquid ratio were first optimized by Box-Behnken design.The results reveal that under optimum conditions([H_(3)PO_(4)]=2 mol/L,T=80℃,and S/L=1:10 g/mL) the leaching efficiencies of Ni,Co reach 98.1% and99.3%.While La,Ce,and Nd elements remain in the leaching residue as(La,Ce,Nd)PO_(4) with yields of 98.2%,98.6%,and 99.6% for La,Ce,and Nd,respectively.Afterward,the(La,Ce,Nd)PO_(4) is leached with HCl acid,then the rare earth oxalate was precipitated using oxalic acid at a pH of 1.8 and then the product was calcined at 800℃ for 2 h in order to synthesize the(Nd,La,Ce)_(2)O_(3).The analysis using scanning electron microscopy(SEM) coupled with energy dispersive X-ray spectroscopy(EDX) confirms the homogeneity of(Nd,La,Ce)_(2)O_(3) particles that have two morphologies,i.e.,flower and sticks with a particle size between 3and 6 μm.The unit cell parameters of(Nd,La,Ce)_(2)O_(3) were calculated after Rietveld refinement of the XRD patterns,in the space group of Fm-3m are a=b=c=0.57921 nm and the volume equal to 0.194322 nm^(3).

Preparation of high-purity tellurium powder by hydrometallurgical method

This hydrometallurgical method consists of oxidation leaching, sulfide impurities removing, and sulfur dioxide reduction. The crude tellurium powder was treated by H2Oa oxidation for 2.0 h at pH 2.5 when adding 50 ml H2O2 （30 %） per 100 g raw material, a tellurium recover rate around 91% is achieved. The tellurium leaching ratio can reach 98.9 % under 3.75 mol.L-1 NaOH concentration in liquid-solid ratio of 5：1 at 80 ℃ for 1.5 h. The overall separation of tellurium and other heavy metals is optimum at sulfide dosages of about 1.1 times of the theoretical values. The removal rates of Ag, Ni, Pb, and Cu from the solution are greater than 99.8 %, and As and Se removal rates are 98.6 % and 97.2 %, respectively. Over 99.5 % tellurium can be recovered by SOu reaction when the operation is conducted at 85 ℃ in 6 mol.L-1 HC1 solution. The tellurium powder with size of 〈5 μm and purity of 〉99.999 % is obtained.

A hydrometallurgical method of energy saving type for separation of rare earth elements from rare earth polishing powder wastes with middle fraction of ceria

This study described a hydrometallurgical method to investigate the separation of rare earth elements（REEs）from rare earth polishing powder wastes（REPPWs）containing large amounts of rare earth oxides with a major phase of CeO2 and minor phases of La2O3,Pr2O3,and Nd2O3 using a process devised by the authors.The suggested approach consisted of five processes：the synthesis of NaR E（SO4）2·xH2O from rare earth oxides in Na2SO4-H2SO4-H2 O solutions（Process 1）,the conversion of NaR E（SO4）2·xH2O into RE（OH）3 using NaO H（Process 2）,and the oxidation of Ce（OH）3 into Ce（OH）4 using air with O2 injection（Process 3）,followed by Processes 4 and 5 for separation of REEs by acid leaching using HCl and H2SO4,respectively.To confirm the high yield of NaR E（SO4）2·xH2O in Process 1,experiments were carried out under various Na2SO4 concentrations（0.4–2.5 mol/L）,sulfuric acid concentrations（6–14 mol/L）,and reaction temperatures（95–125 oC）.In addition,the effect of the pH value on the separation of Ce（OH）4 in HCl-H2 O solutions with Ce（OH）4,La-,Pr-,and Nd（OH）3 in Process 4 was also investigated.On the basis of above results,the possibility of effective separation of REEs from REPPWs could be confirmed.

Solvent Extraction in Hydrometallurgy: Present and Future

During the past 10 years, there have been incremental advances in the application of solvent extraction to process hydrometallurgy. The most cited areas in the literature include chemistry, chemical engineering, pilot plants, and plant operation. Within these areas, there were considerable interest in synergism, diluents, degradation, contactors, surfactants, hydrometallurgical applications, environmental and secondary applications, and health and safety. The summary to the present is followed by a prediction for the future in the above areas of interest. These include the use of speciation; improved understanding of the role of surfactants on the system; optimization through modelling, pilot plants, and contactor selection; improvements in plant operation; further new applications; and plant safety. The review has indicated that considerable knowledge is now available to optimize and improve on process design and plant applications.

Recent advances in the recovery of transition metals from spent hydrodesulfurization catalysts

Hydrodesulfurization(HDS)catalysts are widely used in petrochemical industries,playing a crucial role in desulfurization process to get high-quality oil.The generation of Al-based spent HDS catalyst is estimated to be 1.2×105 tons per year around the world.The spent HDS catalysts have been regarded as an important secondary resource due to their abundant output,considerable metal value,and regeneration potential;however,if improperly handled,it would severely pollute the environment due to high content of heavy metals.Thus,the recovery of valuable metals from spent HDS catalysts is of great importance from both resource utilization and environmental protection points of view.In this work,recent advances in the spent HDS catalyst treatment technologies have been reviewed,focusing on the recovery of valuable transition metals and environmental impacts.Finally,typical commercial processes have been discussed,providing in-depth information for peer researchers to facilitate their future research work in designing more effective and environmentally friendly recycling processes.