Stripping Isotherms Research Articles

Influence of ionic liquid (R4PSCN) for selective separation and recovery of copper from spent Cu[sbnd]Cr catalyst leach liquor

Separation and recovery of copper (Cu) from sulphate mediated CuCr spent catalyst leach solution through solvent extraction approach has been systematically investigated. A number of Ionic Liquid (IL) and other conventional extractants were used while investigating the selectivity and efficient extraction tendency of either IL or extractants towards Cu(II). In context of copper extraction efficiency, the adopted organic reagents followed the descending order: R4PSCN > R4PD > R4PCy > Cyphos 101 > Aliquot 336 > D2EHPA > Cyanex 272. The extraction behavior of Cu(II) was established based on slope analysis method. From the results it was noticed that extraction occurs through a cation exchange mechanism with association of a mole of Cu(II) per mole of R4PSCN. The plot of log D vs. log [R4PSCN] yield a linear relationship with a slope close to 4 which is used to propose extraction reaction mechanism/ stoichiometry. The nature of complex between Cu(II) and IL was further examined using FTIR analysis of the loaded organic phase with the diluent. Mc-Cabe Thiele diagram was constructed to predict quantitative extraction of Cu(II) which revealed the need for two stages at aqueous to organic (A:O) phase volume ratio of =3:1. The stripping isotherm constructed at optimum NH4OH concentration (0.4 M) suggests the need for two stages at O:A phase volume ratio of = 2:1 for complete stripping of copper with regeneration of R4SCN for further use. Both isotherm conditions were validated by 6 cycles of counter current simulation (CCS) study for obtaining the desired amount of Cu(II) loaded R4SCN (during extraction) and/or stripped copper solution (during stripping). Overall copper enrichment was ∼6 fold leading to produce a copper(II) solution of 48 g/L from 6 g/L Cu(II). The stripped solution was subjected to crystallization study to produce copper sulphate crystals of high purity and was confirmed by XRD analysis of crystal phases.

Solvent Extraction with Cyanex 923 to Remove Arsenic(V) from Solutions.

The removal of harmful arsenic(V) from aqueous solutions using Cyanex 923 (solvation extractant) was investigated using various experimental variables: equilibration time, the acidity of the aqueous phase, temperature, extractant and arsenic concentrations, and O/A ratio. Cyanex 923 extracted As(V) (and sulfuric acid) from acidic solutions; however, it could not be used to remove the metal from slightly acid or neutral solutions. The extraction of arsenic is exothermic and responded to the formation of H3AsO4·nL species in the organic phase (L represents the extractant, and the stoichiometric factor, n = 1 or 2, depends on the acidity of the aqueous phase). Extraction isotherms are derived from the experimental results. Both arsenic and sulfuric acid loaded onto the organic phase can be stripped with water, and stripping isotherms are also derived from the experimental results. The selectivity of the system against the presence of other metals (Cu(II), Ni(II), Bi(III), and Sb(III)) is investigated, and the ability of Cyanex 923 to extract As(V) and sulfuric acid compared to the use of other P=O-based solvation reagents, such dibutyl butylphosphonate (DBBP) and tri-butyl phosphate (TBP), is also investigated.

Environmental friendly approach for selective extraction and recovery of molybdenum (Mo) from a sulphate mediated spent Ni–Mo/Al2O3 catalyst baked leach liquor

Solvent extraction separation of molybdenum (Mo) from the sulphate mediated leach solution bearing Aluminium (Al) and Nickel (Ni) was carried out using N-Methyl-N, N, N-tri-octyl-ammonium chloride. Extensive investigation for extraction study molybdenum in the function of time, Eq.pH, extractant concentration, diluents, temperature, strip solution concentration and phase ratio(A:O) for both extraction and stripping was examined to attain a suitable condition on its selective and enriched extraction. As per the equilibrium study and increasing trend of Eq. pH (pHe) at the correspondence initial pH, it was apparent about association of 1 mol of H+ ion during extraction which with was further supported on extraction of Mo as HMO4- at the pHe of 3.48. The association of 1 mol of exrractant during the extraction of Mo was also well evident from the slope analysis study. This indicates about anion exchange phenomenon due to Cl− ion of the N-Methyl-N, N, N-tri-octyl-ammonium chloride (extractant) with HMo4− from aqueous phase during complex formation reaction. The FTIR of the organic sample before and after extraction further confirms in support of the complex formation of the molybdenum with the extractant during extraction. The extraction isotherm was constructed at optmum extraction condition: pHe of 3.48 with 0.08M N-Methyl-N, N, N-tri-octyl-ammonium chloride predicts on need of 2-counter current stages for quantitative extraction of Mo at A:O = 3:1. To investigate the regeneration behaviour of adopted extractant along with enriched stripping of molybdenum, ammoniacal reagents were used in stripping study. The stripping of Mo showed promising and efficient using the mixture of the ammoniacal reagents (NH4OH + NH4Cl) over the either of the solo reagents. The stripping Mc-Cabe Thiele diagram was plotted using 2M NH4OH + NH4Cl ensures on quantitative stripping of Mo at SO: SS = 2:1 at 2 no. of stages. Both extraction and stripping isotherm results are validated at predicted isotherm conditions by 6-cycles counter current simulation (CCS) study leading to obtain 6-fold enrichment of Mo in stripped solution phase. The subsequent enriched content of Mo (∼60 g/L) in stripped solution phase was precipitated out followed by calcinations 400 °C to obtain a high pure MoO3. The recovered calcined product as MoO3 resulted through the proposed processing approach was as ascertained from XRD analysis.

Zinc recovery from dilute ammoniacal media using an integrated solvent extraction and electrolysis process

Zinc(II) was recovered from dilute ammoniacal media through an integrated process combining solvent extraction and electrolysis with ammonia stripping. Zinc ions were firstly enriched into organic phase at pH 7.56 through synergistic extraction between β-diketone and TBP or Cyanex 923. The concentration of extracted zinc(II) increased at pH < 7.56, but clearly decreased at pH 7.56–9.98. The extracted zinc species could be effectively stripped from the loaded organic phase using ammoniacal liquor at pH 9.5, because the ammonia stripping process followed an trend opposite to the extraction process. The extraction and ammonia stripping isotherms verified that Zn(II) concentration can be increased from 1.3 g/L to >56 g/L by using β-diketone and Cyanex 923. Metallic zinc can be obtained by direct electrolysis from the ammoniacal stripping solution. The presence of small amounts of the dissolved extractant molecules can improve the crystallization of zinc deposits. A gelatin additive was used to smoothen the morphology of zinc deposits and refine their crystalline structure. These results indicate that the proposed integrated process will facilitate the recovery of various zinc-bearing primary and secondary resources in ammoniacal media.

Extraction of Uranium(VI) Ions from Sulfate Medium Using Synthesized o-(1-{(E)-[1-(o-Hydroxyphenyl)ethylidene]-hydrazono}ethyl)phenol

A new Schiff base extractant, o-(1-{(E)-[1-(o-hydroxyphenyl)ethylidene]hydrazono}ethyl)phenol (HPEHEP), was synthesized to separate and preconcentrate U(VI) ions from sulfate solution. Various instrumental techniques such as elemental analysis, FTIR, and 1H NMR were employed for full characterization of the synthetic extractant. Analysis of the traditional log D-log [extractant concentration] and log D-pH dependences shows that the uranium ions were extracted as a complex with the ligand: metal ratio of 2: 1, containing one ionizable hydrogen ion. The uranium extraction and stripping conditions have been experimentally optimized. From the extractant effects, 1.86 × 10−2 M HPEHEP was found to be suitable for the U separation. The thermodynamic study indicates that the extraction of uranium(VI) from sulfate medium is an exothermic process (ΔH = −9.87 kJ mol−1). The construction of extraction and stripping isotherms shows that three theoretical stages will be sufficient for countercurrent treatment. The tolerance limits for several metal ions with the synthesized Schiff base extractant were calculated and gave high tolerance limit. The optimum parameters of solvent extraction were finally applied to sulfate leach liquor.

Solvent extraction and stripping of zinc from synthetic chloride solution in presence of manganese and cadmium as impurities

In this research work, solvent extraction and stripping of zinc ions from a Zn-Mn-Cd-bearing solution was investigated using D2EHPA as the extractant in a chloride medium. The efficiency of the extraction and stripping stages was evaluated separately, and different parameters such as the pH, extractant concentration, reaction temperature, and contact time were studied. Based on the results obtained, 97% of zinc, 14% of manganese, and 3% of cadmium were extracted at pH = 2.5, 10% (v/v) of D2EHPA, and 40 °C from the solution containing 5 g L-1 of each metal ion. The stripping isotherms of zinc, manganese, and cadmium at different pH values showed that manganese and zinc were stripped at two different pH values. Thus more than 70% of manganese and more than 90% of zinc were stripped at pH = 2.5 and pH = 0.5, respectively. Kinetic studies indicated that the extraction and stripping of zinc in the first 0.5-1 minute was high. The McCabe–Thiele diagrams showed that two stages of extraction and two stages of stripping in the continuous counter-current flow condition were adequate to separate zinc from Mn and Cd. The dominant Zn species extracted by D2EHPA was ZnCl+, and the values for the thermodynamic parameters ΔHo, ΔSo, and ΔGo were 25.65 kJ mol−1, 79.20 J K−1 mol−1, and 0.86 kJ mol−1, respectively, which showed that the reaction was endothermic at equilibrium.

Extraction of uranium from carbonate solution using synthesized Schiff base and its application for spectrophotometric determination

A new Schiff base extractant, O-[1-(2-pyridylimino) ethyl] phenol (PEPh), was synthesized to separate and pre-concentrate U(VI) ions from carbonate solution prior to its spectrophotometric determination. Various instrumental techniques such as elemental analysis, FTIR, and 1H NMR analysis were employed for full characterization of the synthetic extractant. Analyses of the traditional log10D versus log10 extractant concentrations and versus pH reveal that the uranium ions were extracted as a complex that is characterized by having a ligand: metal ratio of 2:1 and one ionizable hydrogen ion. The operating extraction and stripping conditions of U(VI) in the present study have been experimentally optimized. From the extractant effects, 0.05 M synthesized PEPh was found suitable for the separation of U(VI). The thermodynamic study indicates that the extraction of uranium(VI) from carbonate medium is an exothermic process (ΔH = − 17.08 kJ mol−1). The construction of extraction and stripping isotherm showed that three theoretical stages would be indicated for countercurrent treatment. The tolerance limits for several metal ions on synthesized Schiff base extractant were calculated and gave a high tolerance limit. The optimum parameters of solvent extraction were applied for the spectrophotometric determination of U(VI) in different carboniferous rock using Arsenazo III with accurate results.

Identification and regeneration of degradation products from phenolic hydroxyoxime-based extractant in long-term copper solvent extraction plant

The phenolic hydroxyoxime-based extractant has been discovered to degrade gradually in commercial copper solvent extraction plant. The main degradation products occurred through hydrolysis rather than oxidation or Beckmann rearrangement, which were identified as 1-(2-hydroxy-5-nonylphenyl)propan-1-one and 5-nonyl salicylaldehyde through instrumental analysis. The degradation products could reduce the extraction isotherm, the stripping isotherm and the transfer of copper. Moreover, the extractant regeneration of 5-nonyl salicylaldoxime from 5-nonyl salicylaldehyde was achieved with hydroxylamine sulfate. It was observed that the copper loading capacity of regenerated extractant increased by 64%, compared to the copper loading of untreated hydroxyoxime extractant.

Extraction of indium(III) from sulphuric acid medium by the ionic liquid (PJMTH+HSO4−)

The extraction of indium(III) from acidic sulphuric solution by the ionic liquid (PJMTH+HSO4−) was investigated. This ionic liquid was generated by reaction of the primary amine Primene JMT (PJMT) and sulphuric acid solutions. The metal extraction was investigated under various experimental conditions: equilibration time, temperature, metal and sulphuric acid concentrations in the aqueous feed and extractant concentration in the organic solution. Also, the selectivity of the present system against the presence of other metals in the aqueous feed was examined. Indium stripping is effectively done by the use of sulphuric acid solution. Extraction and stripping isotherms were generated within this work.

Complete removal of trace vanadium from ammonium tungstate solutions by solvent extraction

The complete removal of trace vanadium from ammonium tungstate solutions by solvent extraction using a quaternary ammonium salt with bicarbonate type as extractant was investigated. The effects of organic composition, equilibrium pH and A/O ratio on the extraction and stripping were studied. The metal extraction and stripping isotherms were plotted and the simulation multi-stage counter current extraction and stripping tests were conducted. The results showed that the vanadium can be more easily extracted over tungsten from ammonium tungstate solutions, dropping vanadium to 0.004 g/L with tungsten loss below 5% after six-stage counter current extraction with an organic solvent consisting of 1% (v/v) Aliquat336 and 5% (ν/ν) 2-octanol and a feed containing 100.0 g/L W(VI) and 0.42 g/L V(V) with an A/O ratio of 1/1.25 at pH 8.74 and 25 °C for 10 min. The extracted vanadium(V) species of V2W4O194− in loaded organic solution was identified by the combination of thermodynamic analysis and saturation methods, and FTIR spectral analysis. The vanadium(V) in loaded organic was easily stripped and enriched using 2 mol/L NaOH solution with an A/O ratio of 1/15 in a four-stage counter current stripping, and the stripped organic could also be recycled to extraction after regeneration with ammonium bicarbonate solution.

Solvent Extraction and Separation of Thorium(IV) from Chloride Media by a Schiff Base

The Schiff base extractant, (E)-4-(2-hydroxyethylimino)pentan-2-one (AcEt), for thorium(IV) ions was characterized in methylene chloride in chloride media. Analyses of the conventional log10 D versus pH and versus log10 thorium ion concentration plots of the extraction equilibrium data reveal that the thorium(IV) ions were extracted as a complex that is characterized by having one ionizable hydrogen ion and a metal:ligand ratio of 1:1. The effects of contact time, A:O phase ratio and temperature on the extraction and stripping were studied. Extraction and stripping isotherms were constructed to determine the theoretical stages of the extraction and stripping processes. The thermodynamic parameters Gibbs energy (∆G°), enthalpy (∆H°) and entropy (∆S°) changes associated with the extraction processes were evaluated. Finally, the optimum parameters of solvent extraction were applied to a chloride leach liquor.

Separation of Co(II) and Ni(II) from chloride leach solution of nickel laterite ore by solvent extraction with Cyanex 301

A hydrometallurgical process was developed to recover Co(II) and Ni(II) from the chloride leach liquor of laterite ore. Most of Co(II) and Ni(II) together with a small amount of Al(III) were selectively extracted over other elements by Cyanex 301 from the feed solution at pH 1 which contained Co(II), Ni(II), Al(III), Ca(II), Mg(II) and Mn(II). From the loaded Cyanex 301, Co(II) and Al(III) were selectively stripped by 3 M HCl solution, and then Ni(II) was completely stripped by 10M HCl solution. The McCabe-Thiele plots for the extraction and stripping isotherms were constructed. Batch simulation experiments for the counter-current extraction and stripping indicated that the recovery percentage of Co(II) and Ni(II) was 92.6 and 95.7%, respectively. Moreover, the purity of Ni(II) in the stripping solution was reached 99.5%. A process flowsheet for the recovery of Co(II) and Ni(II) from the laterite leach liquor was proposed.

Direct enrichment of zinc(II) from and into ammoniacal media with commercialLIX84I

Abstract Solvent extraction of zinc(II) from and into ammoniacal media has been investigated using commercial LIX84I extractant. The effects of aqueous solution pH, total ammonia concentration and temperature on extraction of zinc(II)and ammonia stripping of loaded organic phases were examined. The extraction and stripping behaviors of zinc was also compared in the absence and presence of tributyl phosphate (TBP). The results indicate that LIX84I presents a good potential for zinc extraction in the ammonical solution. However, TBP has an antagonistic effect on zinc extraction with LIX84I. The extraction behavior of Zn(II) presents a special swing phenomenon in the both cases with and without TBP. The slope analysis and IR spectra indicate that each zinc ion can coordinate with two LIX84I molecules, whereas TBP molecules could bond with the LIX84I molecules, thus depressing zinc extraction. The zinc loaded organic phases can be effectively stripped with the ammoniacal media, especially increasing the ammonia concentration. Zinc stripping is more easy for the mixed system with TBP than the individual LIX84I system. Moreover, the extraction of zinc is an exothermic process, whereas the ammonia stripping of zinc is an endothermic process. The extraction and stripping isotherms indicate that the direct enrichment of zinc(II) from and into ammoniacal media can be achieved with the commercial LIX84I. These results are helpful for the hydrometallurgical recovery of zinc from the non-traditional resources.

Solvent extraction fractionation of Li-ion battery leachate containing Li, Ni, and Co

Abstract In this research, the separation of Li, Ni, and Co by solvent extraction was studied from synthetic Li-ion battery waste leachate. The purpose was to propose a process for producing all the metals with over 99.5% purities, as the purity demands for battery grade metals are high. Emphasis was also placed on obtaining pure Li raffinate in the early stage of the process, as societal interest in Li is growing rapidly. Thus, the purpose was to first extract Co and Ni selectively yielding pure Li raffinate, and consequently separating Co and Ni as pure products in the stripping stage. The equilibrium behavior of the separation system was studied by constructing the pH isotherms as well as loading and stripping isotherms. Bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and (2-ethylhexyl)phosphonic acid mono-2-ethylhexyl ester (PC-88A) were used as extractants, both as unmodified and modified with 5% v/v TOA or TBP. Based on the equilibrium results, bench-scale continuous counter-current separation experiments were designed and conducted using 1.0 M Cyanex 272 modified with 5% v/v TOA. Co and Ni were loaded in two stages from the sulfate feed solution containing 2.8 g/L of Li, 14.4 g/L of Co, and 0.5 g/L of Ni. In this step, over 99.6% yields for Co and Ni were achieved, giving 99.9% pure Li raffinate. However, 17–26% of Li was co-extracted, but efficient scrubbing with NiSO 4 was designed with equilibrium experiments and demonstrated in continuous operation. In the stripping step, 99.5% pure aqueous Ni solution and 99.2% pure organic Co solution were obtained using two counter-current stages. Adding one more stage increased the Ni and Co purities to 99.7 and 99.6%, respectively. In addition to the high purities of the metals, the suggested process has fewer process steps compared to previously suggested flowsheets for similar fractionation.

Stripping of titanium from TBP-decanol phase

The stripping of titanium from TBP-decanol phase with hydrochloric acid has been investigated. The results showed that the stripping rate of titanium increased with decreased hydrochloric acid concentration in the aqueous phase, decreased organic and aqueous phase ratio and increased stripping temperature. Extracted titanium was easy to strip and 0.5 mol/L hydrochloric acid was suitable stripping agent. The kinetics of the stripping process was fast, since the equilibrium was reached in 10 minutes. The extraction and stripping isotherms showed that through extraction and stripping titanium (IV) was separated and enriched as about five fold. The simulated extraction and stripping of titanium (IV) in leaching solution of blast furnace slag were proceeded.

Solvent Extraction of Scandium from the Waste Solution of TiO2 Production Process

Extraction and stripping properties of Sc3+ were investigated by using a mixed extractant of Versatic Acid 10 (VA10) and Tri-n-butyl phosphate (TBP). The effect of adding TBP to VA10 was considered by analyzing the binding state of VA10 and TBP by FT-IR. Solvent extraction of scandium from an aqueous solution of Sc3+–Ti4+–Zr4+, which simulated waste water from the titanium oxide manufacturing process, the Bayers process and others, was performed, and the separation factor of Sc3+ over Ti4+ and Zr4+ was investigated. To clarify the operating conditions of a countercurrent multistage process for Sc3+, McCabe–Thiele analysis was applied to the extraction isotherm and stripping isotherm of Sc3+. The extraction pH of Sc3+ was found to shift to higher pH, and Sc3+ was stripped at a lower concentration of H2SO4 by adding TBP to VA10. Addition of TBP to VA10 suppresses the extraction of Sc3+ and promotes the stripping of Sc3+. IR spectra of the organic phase suggested that the dimeric portion of VA10 formed hydrogen bonds with TBP. The extractions of Sc3+, Ti4+ and Zr4+ were 77, 3 and 8%, respectively. The separation factors of these metal ions were βSc/Ti = 100 and βSc/Zr = 38 at pH4.6 on extraction with VA10 + TBP from aqueous solutionof Sc3+–Ti4+–Zr4+. Stripping efficiency of 100, 8 and 22% could be achieved for Sc3+, Ti4+ and Zr4+, respectively by using 0.5 mol/dm3 H2SO4. From these results, it was possible to separate Sc3+from impurities such as Ti4+ and Zr4+ by countercurrent multistage extraction, and Sc3+ was recovered by one-stage stripping with 0.5 mol/dm3 H2SO4. Extraction of Sc3+from the dilute aqueous solution containing 500 mg/dm3 of Sc3+reached 99% at the flow ratio (A/O) = 1.01 in the two-stage countercurrent extraction, and Sc3+ in the organic phase was stripped to attain a six-fold concentration by applying one-stage stripping with flow ratio of (O/A) = 6.00.

Development of a separation process for the selective extraction of hafnium(IV) over zirconium(IV) from sulfuric acid solutions by using D2EHPA

A new process for the separation of Zr(IV) and Hf(IV) from sulfuric acid solution by selective extraction and stripping was proposed. Firstly, Hf(IV) was preferentially extracted by di-2-ethylhexylphosphoric acid (D2EHPA) from moderate sulfuric acid solutions. From the loaded D2EHA, co-extracted Zr(IV) was selectively stripped by strong sulfuric acid solution with a separation factor of 10, leaving only Hf(IV) in the stripped D2EHPA. Hafnium(IV) was then completely stripped by oxalic acid solution and thus D2EHPA was regenerated. The McCabe–Thiele plots for the extraction and stripping isotherms were constructed and the results were verified by the simulated cross-current extraction and stripping experiments. Zirconium(IV) solutions of high purity were obtained in the extraction raffinate and sulfuric acid stripping solution, while Hf(IV) was present in the oxalic acid stripping solution.

A novel strategy achieving enrichment of metal values from and into ammoniacal solutions

A novel strategy has been proposed to achieve enrichment of metal values from and into ammoniacal solutions through solvent extraction. The extraction equilibria of Cu(II), Ni(II) and Zn(II) in ammoniacal sulfate solution have been examined with β-diketone in the pH range of 6–12. The ammonia stripping behaviors of three metal ions have been studied by consideration of total ammonia, pH and temperature. The results indicate that a special swing phenomenon was found for both extraction and ammonia stripping processes. The loaded organic phases can be successfully stripped with ammoniacal solutions by adjusting total ammonia concentration and pH. Zinc and nickel are more easily stripped than copper. Increasing temperature is beneficial for the ammonia stripping of zinc and nickel but adverse for copper, thus potentially improving the Zn/Cu and Ni/Cu separation. The ammonia stripping isotherm shows that zinc can be efficiently enriched with two counter current stages. Moreover, there is no significant loss of organic phase during stripping. Therefore, direct enrichment of metal values through ammonia stripping has a good prospect for the integrated extraction and electrowinning circuit throughout ammoniacal systems.

NEODECANOIC ACID AS EXTRACTANT OF SELECTED NON-FERROUS METALS

The paper presents results of studies on extracting properties of neodecanoic acid (Versatic 10) solutions. Neodecanoic acid was diluted in Exxsol D80 AZ to three concentrations: 7.5, 15, and 30 % ( v /v). Tests were conducted using sulphate(VI) solutions of six ions: Zn(II), Ni(II), Cu(II), Co(II), Cd(II), Mn(II) and a nitrate(V) solution of Pb(II). All the aqueous solutions were prepared as 0.1 M concentration. For all combinations of the used solutions (organic and aqueous), direct methods of measuring and recording the pH of the biphasic mixture have been applied. The degrees of ions extraction, depending on equilibrium pH were also presented in the paper. Extraction and stripping isotherms of selected ions and organic phase were plotted for 7.5 and 30 % ( v /v) of extractant solutions and Zn(II), Ni(II) and Cu(II) ions.

Development of a hydrometallurgical process for the recovery of calcium molybdate and cobalt oxalate powders from spent hydrodesulphurization (HDS) catalyst

Abstract In order to recover molybdenum and cobalt from spent hydrodesulphurization (HDS) catalysts, a hydrometallurgical process consisting of leaching, solvent extraction and precipitation was developed. The Mo and Co in the spent HDS catalysts were leached in HCl solution. Mo was first separated by solvent extraction with TBP and the Mo free raffinate was then contacted with TEHA to separate Co. Stripping of Mo and Co from the loaded organic phases was carried out using dilute HCl solution and distilled water. The extraction and stripping isotherms were constructed to get the required number of multi-stages. 99.8% of Mo and 99.4% of Co were recovered by solvent extraction and the purity of Mo and Co stripping solutions was found to be 99.99%. CaMoO 4 powders with uniform morphology were obtained by adding calcium chloride to the Mo stripping solution at pH 5.0 and 90 °C. The optimum conditions for the formation of uniform rod-like CoC 2 O 4 particles by adding oxalic acid were at pH 5.0 and 60 °C. The overall recovery of Mo and Co from spent HDS catalyst was 96% and 93%.