Leaching Of Co Research Articles

Leaching of Co, Mn and Ni Using H2O2 in Sulfuric Acid Medium from Mobile Phone LIBs

From the economic point of view, spent lithium-ion batteries (LIBs) are a precious resource that contains metals such as Co, Mn and Ni. On the other hand, environmental considerations and repetitious exploitation of natural resources, the so-called primary resource, have drawn significant attention to recycling resources. Regarding the special properties of Co, Mn and Ni, the leaching method was used to recover these metals from LIBs. For this purpose, sulfuric acid due to appropriate efficiency in the presence of H2O2 as a reducing agnet was chosen. To obtain optimum conditions of Co, Mn and Ni leaching, effective parameters on leaching steps such as sulfuric acid concentration, pulp density and H2O2 vol% were investigated. The results of ICP analysis showed that leaching of Co, Mn and Ni in the presence of 1 M sulfuric acid and 15% H2O2 (v/v) at a pulp density of 50 g/L had high efficiency, and more than 99 wt% of metals was simultaneously leached. In the absence of H2O2, leaching percent of Co, Mn and Ni was not significant and it was attributed to various oxides present in LIBs that include different valances.

An improved process methodology for extracting cobalt from zinc plant residues

Zinc plant residue contains valuable metals that can be reused as a source for obtaining these metals. This paper describes the use of sodium thiosulfate (Na2S2O3) in leaching of Co and Mn from zinc plant residue, and purifying the leach solution in order to obtain a pure solution of Co(II). After dissolution of zinc using sulfuric acid, Co and Mn were dissolved in H2SO4 in the presence of a reducing agent. The effects of temperature, acid percentage, type and concentration of reducing agent on dissolution were studied. The results for sodium thiosulfate showed the dissolution of 90.7% and 87.6% Co and Mn, respectively at 65 °C, with an acid concentration of 5% and sodium thiosulfate concentration of 6 g/L. The corresponding results in the presence of H2O2 as a reducing agent are 94.7% Co, 96.3% Mn at 50 °C with the same acid and reagent concentration. An analysis of variation (ANOVA) on the corresponding data was performed. A new correlation as a function of reducing agent yielding the recovery for Co and Mn was derived. Moreover, the purification process of metals was investigated which was a combination of the precipitation method for removing iron, and the solvent extraction for separating Co(II) and Mn(II). The factors influencing solvent extraction i.e., pH, organic concentration, and organic/aqueous ratio were optimized. Finally, two processes for extracting Co and Mn from the hot filter cake (HFC) were proposed and compared.

A Citric Acid/Na2S2O3 System for the Efficient Leaching of Valuable Metals from Spent Lithium-Ion Batteries

Recycling of valuable metals from spent lithium-ion batteries (LIBs) appears inevitable for both environmental protection and resource recovery. In the present study, an efficient hydrometallurgical leaching of Co and Li from cathode materials of spent LIBs using a citric acid/sodium thiosulfate (Na2S2O3) system is explored. The effects of citric acid and Na2S2O3 concentrations, leaching time, temperature, and the solid/liquid (S/L) ratio on the leaching processes are also examined. With the exception of the S/L ratio, the increase of citric acid concentration, Na2S2O3 concentration, leaching time, and temperature all have positive effects on the leaching of Co and Li. Ultimately, approximately 96% of Co and 99% of Li are recycled from the spent LIBs in this citric acid/sodium thiosulfate system under the leaching conditions of an S/L ratio of 20 g l−1, concentration of Na2S2O3 of 0.3 M, concentration of citric acid of 1.2 M, leaching time of 30 min, and leaching temperature of 70°C. The Avrami equation is well fitted by the data of the leaching processes, and model equations are built to describe the leaching of Co and Li. Furthermore, pure sulfur can be obtained as a by-product during the leaching process, and SO2 produced during the reaction is easily collected as a raw material for industrial production of sulfuric acid. The present study represents a promising process for hydrometallurgical recovery of valuable metals from spent LIBs.

Intermetallic PtCo Catalysts for Fuel Cell Applications

Conventional catalysts for the cathode reaction in polymer electrolyte fuel cells (PEFCs) are based on Pt and random alloys of Pt with base metals. Addition of base metals such as Co to nanostructured Pt catalysts is known to enhance oxygen reduction reaction (ORR) activity, but poor stability of Co under the aggressive conditions of high potential and low pH found in the cathode of PEFCs limits the enhancement provided by Co. Recently, we have developed several varieties of L10 ordered PtCo nanoparticle catalysts that exhibit remarkably enhanced performance and durability. Several factors, including particle size, Co content, degree of ordering, Pt shell thickness, and nanoparticle-support interactions are critical in determining performance and durability. Synthetic procedures developed at LANL have enabled preparation of L10-PtCo with small particle size, high electrochemical surface area, good dispersion on the carbon-based support, and high performance in PEFC cathode testing under H2/air. These intermetallic particles retain high Co content with L10 ordering even after 30,000 square wave potential cycles between 0.6 and 0.95 V in membrane electrode assemblies (MEAs). Content of Co is a key factor controlling ORR kinetic performance. Furthermore, leaching of Co into the membrane and electrode ionomer can result in performance degradation due to cationic poisoning. Therefore, any reduction in Co leaching from PtCo catalysts would be helpful. The L10-PtCo structures developed at LANL retain Co content approximately 50% higher than a random PtCo alloy after 30,000 potential cycles in MEA. This excellent resistance to Co leaching is the most important contribution of the L10 structure to providing high durability. Testing of new PtCo catalysts in MEAs is particularly critical to validate their performance and durability under real-world conditions. In addition to discussing the L10-PtCo synthesis, this talk will also describe work at LANL on optimizing the integration of these catalysts into high performance, durable MEAs.

Efficient degradation of tetracycline by heterogeneous cobalt oxide/cerium oxide composites mediated with persulfate

The performance of pure cerium oxide (CeO2) and cobalt oxide (Co3O4) in advance oxidation processes cannot meet the growing pursuit of superior catalytic efficiency. In this study, efficient heterogeneous Co3O4/CeO2 (OE) composites were fabricated by a calcination method to activate persulfate (PS) for tetracycline (TC) degradation. Results showed that OE-2/PS system exhibited the highest TC degradation efficiency (79%), while that of CeO2/PS system and Co3O4/PS system was only 22% and 14%, respectively. Co dispersion and turn over frequency demonstrated the superiority of OE-2 composite. Oxidative sulfate radicals (SO4−) and hydroxyl radicals (HO) generated in the process contributed to the efficient degradation of TC, which was proved by radical scavenging experiment and electron spin resonce experiment. In addition, the high stability and recycling ability of OE-2 composite were proved by the detection of leaching of Co and Ce ions and cycling test.

Separation and recovery of valuable metals from spent lithium ion batteries: Simultaneous recovery of Li and Co in a single step

Abstract Sustainable recovery of metals from spent lithium-ion batteries (LIBs) may be of great significance regarding the conservation of metal resources and alleviation of potential risk towards eco-system. Herein an environmentally benign process was proposed for the recovery of high value-added metals (Co and Li) from typical waste cathode materials (LiCoO2) of spent LIBs using mild tartaric acid as both leaching and precipitating reagent. Leaching results indicate that Co and Li can be effectively separated under experimental conditions of reaction temperature- 80 °C, retention time- 30 min, pulp density- 30 mL/g, reducatant dosage- 3 vol% H2O2 and acid concentration- 0.6 mol/L. After leaching, 98% Co and 97% Li can be recovered as precipitate and Li+ enriched solution, respectively. And the leaching of Co and Li fits well to logarithmic rate model, with apparent activation energy of 34.5 and 29.7 KJ/mol, respectively. In addition, characterization results (i.e. FT-IR, SEM-EDS and TGA-DSC) suggest that Co can be directly recovered as relatively pure cobalt tartrate (C4H4O6Co, with a purity of 96.4%) in leaching residues. This whole process can be a sustainable alternative for the simultaneous recovery of Li and Co from waste cathode materials of spent LIBs.

Close loop separation process for the recovery of Co, Cu, Mn, Fe and Li from spent lithium-ion batteries

Abstract Lithium-ion batteries (LIBs) are essential energy source used in advanced electronic gadgets for getting constant and continuous power supply. Huge amount of spent LIBs are generated after their end use. LIBs contain metals, organics and plastics which require proper treatment before disposal. Keeping in view of stringent environmental regulations, limited natural resources and energy crisis, adopting recycling will not only protect the environment and pacify the gap between demand and supply but also conserve the natural resources. Present paper reports a complete process for the recycling of LIBs to recover metals and materials as value added products fulfilling zero waste concept. Initially, the spent LIBs were crushed and beneficiated by wet scrubbing process to separate cathodic material, plastic and metallic fractions. The cathodic material contained 20% Co and 2.4% Li along with other impurities (Mn, Fe, Cu). The cathodic material obtained from different LIBs were homogenized and put to leaching studies to optimize various process parameters viz. effect of leachant concentration, temperature, time, etc. About 97% Co and 99.99% Li were leached using 2 M H2SO4 and 10% H2O2 at room temperature, in 2 h maintaining pulp density 75 g/L. Kinetics for leaching of Co fitted well with “Chemical reaction control dense constant size cylindrical particles model”, i.e. 1 − (1 − X)1/2 = Kct. The leach liquor obtained was further processed to recover Mn and Fe using (NH4)2S2O8 as a precipitant whereas 99.99% Cu was extracted using LIX 84 IC at eq. pH 2, O/A ratio 1/1 and mixing time 5 min. Further, from the leach liquor depleted with Mn, Fe and Cu, ∼98% Co was extracted using 20% Cyanex 272 at pH 4.8 in 10 min maintaining phase ratio (O/A) 1/1 in two stages, leaving Li in the raffinate. From the pure Co solution, value added products as metal and salt were produced using electrowinning/evaporation/precipitation techniques. The TCLP test of leached residue shows the presence of metals within permissible limit and the effluent generated was treated in an effluent treatment plant (ETP) with standard procedure and recycled to the system. The developed clean process is economical as well as environment friendly and has potential to be translated in industry after scale-up studies.

PtCo Cathode Catalyst Morphological and Compositional Changes after PEM Fuel Cell Accelerated Stress Testing

Development of Pt catalysts alloyed with transition metals has led to a new class of state-of-the-art electrocatalysts for oxygen reduction at the cathode of proton exchange membrane fuel cells; however, the durability of Pt-based alloy catalysts is challenged by poor structural and chemical stability. There is a need for better understanding of the morphological and compositional changes that occur to the catalyst under fuel cell operation. Here, we report in-depth characterization results of a Pt-Co electrocatalyst incorporated in the cathode of membrane electrode assemblies, which were evaluated before and after accelerated stress tests designed specifically to enhance catalyst degradation. Electron microscopy, spectroscopy, and 3D electron tomography analyses of the Pt-Co nanoparticle structures suggest that the small- and intermediate-sized Pt-Co particles, which are typically Pt-rich in the fresh condition, undergo minimal morphological changes, whereas intermediate- and larger-sized Pt-Co nanoparticles that exhibit a porous “spongy” morphology and initially have a higher Co content, transform into hollowed-out shells, which is driven by continuous leaching of Co from the Pt-Co catalysts. We further show how these primary Pt-Co nanoparticle morphologies group toward a lower Co, larger size portion of the size vs. composition distribution, and provide details of their nanoscale morphological features.

Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 2. Ni/MH Battery Performance and Failure Mechanisms

The electrochemical performance and failure mechanisms of Ni/MH batteries made with a series of the Fe-substituted A2B7 superlattice alloys as the negative electrodes were investigated. The incorporation of Fe does not lead to improved cell capacity or cycle life at either room or low temperature, although Fe promotes the formation of a favorable Ce2Ni7 phase. Fe-substitution was found to inhibit leaching of Al from the metal hydride negative electrode and promote leaching of Co, which could potentially extend the cycle life of the positive electrode. The failure mechanisms of the cycled cells with the Fe-substituted superlattice hydrogen absorbing alloys were analyzed by scanning electron microscopy, energy dispersive spectroscopy and inductively coupled plasma analysis. The failure of cells with Fe-free and low Fe-content alloys is mainly attributed to the pulverization of the metal hydride alloy. Meanwhile, severe oxidation/corrosion of the negative electrode is observed for cells with high Fe-content alloys, resulting in increased internal cell resistance, formation of micro-shortages in the separator and eventual cell failure.

Vertical changes of the Co and Mn speciation along a lateritic regolith developed on peridotites (New Caledonia)

Because they can host significant amounts of Co, the Mn-oxides are commonly considered as the major Co-bearing mineral species in lateritic environments. However, little is known about the process leading to the formation and/or the weathering of these Co-rich Mn-oxides. This lack of knowledge is mainly due to the fact that Co concentrations are too low in primary silicates for classical speciation analysis. In this study, we investigated both Co and Mn speciation in a 64m thick lateritic regolith developed upon peridotites in New Caledonia, by combining High Energy Resolution Fluorescence Detection X-ray absorption Near Edge Structure (HERFD-XANES) spectroscopy at the Co K-edge with classical XANES spectroscopy at the Mn K-edge, bulk chemistry (ICP) and mineralogy (XRD). The results obtained provide new insights into the evolution of Co and Mn speciation as a function of the weathering stages. Co and Mn primarily occur as Co(II) and Mn(II,III) in olivine and serpentine in the bedrock. During the first weathering stage, these forms of Co and Mn are progressively oxidized toward Co(III) and Mn(III,IV), which occur mainly as Co(III)-bearing Mn(III/IV)-oxides in the transition between the saprolite and the laterite. In the uppermost lateritic horizons, long-time weathering resulted in a strong leaching of Co and Mn, and the remaining of these elements occurs as Co(II) and Mn(III) substituting for Fe(III) in goethite. This latter scavenging process emphasizes the importance of Fe-oxides for the long-term stabilization of Co and Mn in such deeply weathered laterites.

Leaching and separation of Co and Mn from electrode materials of spent lithium-ion batteries using hydrochloric acid: Laboratory and pilot scale study

The present work is focused on the leaching and separation of Co and Mn from electrode material of spent lithium-ion batteries. The influences of different process parameters like HCl concentration, time, and temperature on the leaching of Co and Mn are studied. Higher than 99% leaching efficiencies of Co and Mn were obtained in 90 min using 1.75 M HCl at 50 °C. In the subsequent precipitation study, Mn was removed selectively from the leach solution by using sodium hypochlorite solution (1.5 times stoichiometric requirement) at a pH of 1.5 in 30 min. X-ray diffraction analysis of precipitated manganese indicate the presence of mixtures of manganese oxides (MnO2, Mn3O4 and Na0.55Mn2O4.1.5H2O). Cobalt in the Mn free solution was precipitated by using sodium carbonate solution after removing the traces amount of Al and Cu. Overall recovery of Mn and Co is 95% and 90%, respectively in pilot scale. The flow sheet proposed for the leaching and separation of Co and Mn is of a simple and efficient technique for the recycling industries.

Synergistic degradation of phenols using peroxymonosulfate activated by CuO-Co3O4@MnO2 nanocatalyst

The development of transition metal based heterogeneous catalysts with efficient reactivity and intensive stability is of great demand in peroxymonosulfate based AOPs in water treatment. Herein, we present a novel approach of creating stable and effective nano-rod catalyst of CuCo@MnO2 with tetragonal structure. A remarkable synergetic effect was found between bi-metallic oxides of Cu and Co: 0.5%Cu-2%Co-MnO2 can efficiently degrade 100% of 30ppm phenol, while 0.5%Cu@MnO2 or 2%Co@MnO2 alone is apparently sluggish for the degradation of organic contaminants. The nanocatalyst retained good stability in recycling tests, during which little leaching of Co and Cu ions can be detected and crystallinity of support α˗MnO2 remained unchanged. Mechanism study indicated that SO4− and OH are accounted to participate the degradation, and the generation of radicals is originated from the interaction of CuCo@MnO2 and PMS through metal site with peroxo species bond. The redox cycle among the active metals (M2+↔M3+↔M2+) and Cu enhanced generation of Co(II)–OH complex are critical for the remarkable performance in CuCo@MnO2/PMS system. Both the synergetic acceleration of catalyst activity and instinct mechanism are highly suggestive to the design of heterogeneous catalysts for the degradation of organic contaminants in PMS based advanced oxidation processes.

Recovery of valuable metals from waste cathode materials of spent lithium-ion batteries using mild phosphoric acid

Sustainable recycling of valuable metals from spent lithium-ion batteries (LIBs) may be necessary to alleviate the depletion of strategic metal resources and potential risk of environmental pollution. Herein a hydrometallurgical process was proposed to explore the possibility for the recovery of valuable metals from the cathode materials (LiCoO2) of spent LIBs using phosphoric acid as both leaching and precipitating agent under mild leaching conditions. According to the leaching results, over 99% Co can be separated and recovered as Co3(PO4)2 in a short-cut process involved merely with leaching and filtrating, under the optimized leaching conditions of 40°C (T), 60min (t), 4 vol.% H2O2, 20mLg−1 (L/S) and 0.7mol/L H3PO4. Then leaching kinetics was investigated based on the logarithmic rate kinetics model and the obtained results indicate that the leaching of Co and Li fits well with this model and the activation energies (Ea) for Co and Li are 7.3 and 10.2kJ/mol, respectively. Finally, it can be discovered from characterization results that the obtained product is 97.1% pure cobalt phosphate (Co3(PO4)2).

Mechanochemical Process Enhanced Cobalt and Lithium Recycling from Wasted Lithium-Ion Batteries

Cobalt (Co) and lithium (Li), rare and valuable elements, are mainly used to prepare lithium cobalt oxide (LiCoO2) for applications in lithium-ion batteries (LIBs). Developing an effective method to recover Co and Li from the waste LIBs is of great significance. In the present study, Co and Li were extracted from pure LiCoO2 powders and the extracted cathode materials powders from the waste LIBs after acid dissolution via a mechanochemical reduction process with iron powders. For pure LiCoO2 powders, the effects of Fe to LiCoO2 mass ratio, rotation speed, and mechanochemical reduction time were examined. These parameters influenced positively the extraction of Co, while they showed negligible effects on the leaching of Li. The X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated a promoted extraction of Li arising from the reduction of particle sizes, magnification of specific surface area, and change of the crystal structure of particles. For high-efficiency leaching of Co by the mechanochemical reduction process with iron powders, X-ray photoelectron spectroscopy (XPS) analysis indicated the changes in the valence state of Co. The actual cathode materials disassembled from the wasted LIBs pretreated by this novel mechanochemical reduction process were also explored. The results indicated that the leaching ratios of Li, Co, Mn, and Ni could reach 77.15%, 91.25%, 100%, and 99.9%, respectively. This novel mechanochemical process would be of great importance for the recovery of valuable metals from waste LIBs.

Ionic Polymer Microspheres Bearing a Co(III) -Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides.

We report a unique strategy to obtain the bifunctional heterogeneous catalyst TBB-Bpy@Salen-Co (TBB=1,2,4,5-tetrakis(bromomethyl)benzene, Bpy=4,4'-bipyridine, Salen-Co=N,N'-bis({4-dimethylamino}salicylidene)ethylenediamino cobalt(III) acetate) by combining a cross-linked ionic polymer with a Co(III) -salen Schiff base. The catalyst showed extra high activity for CO2 fixation under mild, solvent-free reaction conditions with no requirement for a co-catalyst. The synthesized catalyst possessed distinctive spherical structural features, abundant halogen Br(-) anions with good leaving group ability, and accessible Lewis acidic Co metal centers. These unique features, together with the synergistic role of the Co and Br(-) functional sites, allowed TBB-Bpy@Salen-Co to exhibit enhanced catalytic conversion of CO2 into cyclic carbonates relative to the corresponding monofunctional analogues. This catalyst can be easily recovered and recycled five times without significant leaching of Co or loss of activity. Moreover, based on our experimental results and previous work, a synergistic cycloaddition reaction mechanism was proposed.

Recovery of cobalt as cobalt oxalate from spent lithium ion batteries by using glycine as leaching agent

In the article, we are explaining a hydrometallurgical based process on leaching applied to recover Co from spent lithium ion batteries (LIBs). Glycine and ascorbic acid were introduced as leaching reagents and the leaching of Co with a solution containing glycine is investigated. An effective recovery of Co is possible when both glycine and ascorbic acid are used. A condition for achieving a recovery of more than 95% Co has been achieved experimentally by varying the concentrations of leachant and time of the reaction. Leaching with 0.5M glycine, 0.02M ascorbic acid and 0.2g LiCoO2 in a batch extractor, results in a highly efficient recovery of Co within 360min of the processing time at 80°C. This hydrometallurgical process is found to be simple, eco friendly and satisfactory for the recovery of cobalt from spent LIBs.

Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and long term durability of the Fe-Co/NF-GNF catalyst make it a promising ORR electrocatalyst for the fuel cell cathode reaction.

콩고산 코발트 정광으로부터 제조한 매트의 고온고압침출

Abstract Cobalt is abundant only in some countries including Democratic Republic of the Congo. It would be necessary to secure over-seas Co ores and Co extraction technology. Two kinds of matte varying the sulfur content were manufactured by smelting reduc-tion of Co concentrate containing ~8 wt% Co, ~19 wt% Cu, and ~3 wt% Fe. The amount of Co, Cu and Fe was concentratedto 19~21 wt%, 39~41 wt%, and 7~9 wt% respectively in the resulting matte. High-pressure leaching of matte was performedin an autoclave with considering the effect of oxidizing agent, H 2 SO 4 concentration as a lixiviant, and the amount of sulfur addedto the matte. An oxidizing agent (oxygen) is necessary to improve Co leaching efficiency enabling usage of a dilute H 2 SO 4 leach-ing agent. An increase in H 2 SO 4 concentration prevents selective leaching of Co, and the sulfur content in matte has a minorinfluence on the Co leaching efficiency.Key words : cobalt, matte, autoclave, oxidizing agent, leaching · Received : June 5, 2015 · Revised : June 24, 2015 · Accepted : July 29, 2015Corresponding Author : Kyungjung Kwon (E-mail : kjkwon@sejong.ac.kr)Department of Energy & Mineral Resources Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747, KoreaⓒThe Korean Institute of Resources Recycling. All rights reserved. This is an open-access article distributed under the termsof the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permitsunrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.

Acid leaching of heavy metals from contaminated soil collected from Jeddah, Saudi Arabia: kinetic and thermodynamics studies

Urban soils polluted with heavy metals are of increasing concern because it is greatly affecting human health and the ecological systems. Hence, it is mandatory to understand the reasons behind this pollution and remediate the contaminated solid. The removal of heavy metals from contaminated soil samples collected from the vicinity of the sewage lake in Jeddah, Saudi Arabia, was explored. The leaching process was studied kinetically and thermodynamically for better understanding of the remediation process. The results showed that the soil samples were slightly basic in nature, and tend to be more neutral away from the main contaminated sewage lake area. The total metal content in the soil samples was measured using the aqua regia extractions by ICP-OES and the results showed that many of the heavy metals present have significant concentrations above the tolerable limits. In general, the metal concentrations at different sites indicated that the heavy metal pollution is mainly due to the sewage discharge to the lake. The results showed excellent correlation between the concentrations of Co, As, and Hg with the distance from the main contaminated area. The leaching of Co, As, and Hg using 1.0M hydrochloric acid from the soil was studied kinetically at different temperatures and the experimental results were fitted using different kinetics models. The experimental data were best described with two-constant rate and Elovich equation kinetic models. Also, the thermodynamic study showed that the leaching process was spontaneous, endothermic and accompanied with increase in the entropy. In general, the polluted soil could be remediated successfully from the heavy metals using the acid leaching procedure in a short period of time.

Controlled leaching with prolonged activity for Co–LDH supported catalyst during treatment of organic dyes using bicarbonate activation of hydrogen peroxide

The effluents from industries are commonly non-biodegradable and produce various hazardous intermediate products by chemical reactions that have direct impact on environment. In the present investigation, a series of Co–Mg/AL ternary LDH catalysts with fixed Mg/Al ratio were prepared by co-precipitation method. The effect of Co on the activity of the catalyst was monitored on the degradation of methylene blue (MB) as model compound at batch level using bicarbonate activation of H2O2 (BAP) system. On bench level, the best CoMgAl-4 catalyst can completely decolorize both methylene blue (MB) and methylene orange (MO) in short time, while in fixed bed, the catalyst was found stable for over 300h with nearly 100% decolorization and excellent chemical oxygen demand (COD) removal. No leaching of Co was detected for the entire fixed experiment which may be accounted for long life stability and good activity of the catalyst. The ternary LDH catalysts were characterized by AES, XRD, FTIR, BET, and SEM for its compositional, phase structure, optical properties, textural, and surface morphology respectively. The XRD analysis confirmed characteristic pattern of hydrotalcite like structures without impurity phases. The formation of superoxide and hydroxyl radical as ROS was proposed with CoMgAl-4 by radical’s scavengers.