Vanadium, iron and aluminum were recovered from the spent sulfuric acid catalyst with efficiency of 98%, 95% and 85%, respectively by using low temperature sulphuric acid baking followed by leaching. The optimum baking conditions were four grams of concentrated sulfuric acid per ten grams of spent catalyst at 300 ^\circ C for two hours. Sulphuric acid baking followed by leaching was found to be the best and it is more effective in Iron and Aluminum dissolution. Sulfuric acid baking is expected to consume small amount of chemicals and generate much less waste effluents during the separation process of metals with alkali solutions. It is economically favorable, as it avoids us much more environmental contamination

Abdulbake, Mohamedalkhaled

Alouche, Adel

Wahoud, Abdulrahman

Periodica Polytechnica Chemical Engineering

English

Periodica Polytechnica (Budapest University of Technology and Economics)

Ŕ periodica polytechnicaChemical Engineering55/1 (2011) 31–34doi: 10.3311/pp.ch.2011-1.06web: http://www.pp.bme.hu/chc© Periodica Polytechnica 2011RESEARCH ARTICLESulfuric acid baking and leaching ofspent sulfuric acid catalystAbdulrahman Wahoud / Adel Alouche / Mohamedalkhaled AbdulbakeReceived 2010-10-19AbstractVanadium, iron and aluminum were recovered from the spentsulfuric acid catalyst with efficiency of 98%, 95% and 85%, re-spectively by using low temperature sulphuric acid baking fol-lowed by leaching. The optimum baking conditions were fourgrams of concentrated sulfuric acid per ten grams of spent cat-alyst at 300 ◦C for two hours. Sulphuric acid baking followedby leaching was found to be the best and it is more effective inIron and Aluminum dissolution. Sulfuric acid baking is expectedto consume small amount of chemicals and generate much lesswaste effluents during the separation process of metals with al-kali solutions. It is economically favorable, as it avoids us muchmore environmental contamination.KeywordsBaking · Vanadium · Aluminum · Iron · Spent catalystAcknowledgementThe authors would like to express their thanks and appreci-ation to Albaath University for its help and encouragement tocarry out this research. We are very grateful to General Fertil-izer Company (GFC)/Homs for supplying catalyst samples.Abdulrahman WahoudAlbaath University„ P.O. Box 77 Homs, Syriae-mail: awahoud@yahoo.comAdel AloucheMohamedalkhaled AbdulbakeAlbaath University„ P.O. Box 77 Homs, Syria1 IntroductionCatalytic processes have many industrial uses [1, 2], whichis increasing every day. The catalysts deactivate with time andwhen the activity of the catalyst declines below the acceptablelevel, it is usually regenerated and reused [3,4], but regenerationis not always possible [5, 6], and after a few cycles of regener-ation and reuse, the catalyst activity may decrease to very lowlevel and further regeneration may not be economically feasi-ble. The spent catalysts are discarded as solid wastes [7, 8] andtheir contribution to environmental contamination is increasingevery day. The hazardous nature of the spent catalysts is attract-ing the attention of environmental authorities in many countriesand the environmental laws become more severe in recent years.Spent catalysts have been classified as hazardous wastes by theEnvironmental Protection Agency in USA [9, 10]. At the sametime, most of these catalysts contain valuable metals (V, Ni, Mo,Co, etc.) in the form of oxides or sulfides supported on carrierssuch as alumina, silica, etc. Recovery of these metals, many ofwhich in turn consumed in carbon and stainless steel- makingas an alloying agent to produce ferro-alloys and other valuableproducts, is an attractive option [11–13]. Hydrometallurgicalprocesses to recover pure vanadium from sulfate solutions com-ing from leaching of spent catalysts were proposed by meansof solvent extraction with primary aliphatic amine [14] or us-ing organic phase containing di(2-ethylhexyl) phosphoric acidcombined with tributyl phosphate [15]. Recent literature surveyrevealed that large number of hydrometallurgical processes pro-posed wide variety of reagents for leaching of spent catalysts.Several mineral acids and their combination in different con-centrations were used in different processes [16–18]. Amongthe mineral acids, sulfuric acid leaching has certain economicaland operational advantages [19]. Recovery of vanadium pen-toxide from spent sulfuric acid catalysts was reported [20] us-ing a three–step process consisting of acid leaching, oxidationand precipitation. Alkaline leaching is more selective for ironbut dissolves some silica and is more costly in term of reagents[21]. However, in many other instances, leaching with strongmineral acids or alkaline reagents was found to be ineffectivein completely dissolving the catalyst. So, some of alkalic roast-Sulfuric acid baking and leaching of spent sulfuric acid catalyst 312011 55 1vanadium and iron have a good scattering on the alumina-silica support.          Fig (1): The SEM image with EDX spectrum of the spent catalyst 3-2 Sulphuric acid leaching:  Fig. 1. The SEM image with EDX spectrum of the spent catalysting processes were explored and higher dissolution was reportedby using potassium bisulfate [22], but these processes consumelarge excess of the costly reagents and generate large quantitiesof liquid effluents in the down stream. Sulfuric acid baking is ex-pected to be effective at comparatively lower temperature thanalkalic roasting processes and could be lower acid consumptionthan direct sulfuric acid leaching. Therefore, the purpose of thepresent work is to explore an innovative sulfuric acid bakingroute for recovery and complete dissolving of metals in the spentcatalyst.2 Experimental2.1 MaterialsSpent catalyst used in the manufacture of sulphuric acid wassupplied by the General Fertilizer Company GFC Homs /Syria.For consistency, the spent catalyst for all experiments was col-lected from one batch and grounded to a particle size between 1and 2 mm since lower grain sizes did not improve leaching effi-ciencies in preliminary tests. Sulfuric acid used for baking andleaching and all other chemicals employed were of analyticalgrade.2.2 Procedures and apparatusBaking tests were carried out inside a muffle furnace (Carbo-lite). In each experiment 10 g of spent catalyst was mixed withsuitable amount of concentrated sulfuric acid inside a 100 mlporcelain crucible. All leaching tests were carried out in abeacher with a magnetic stirrer placed in a thermostat to controlthe temperature. All baked samples were leached with 100 mlof 2% sulfuric acid solution at 100 ◦C for 1 hour. The mixtureswere filtered with a vacuum filtrating unit. The samples were di-luted and concentrations of metals (V, Fe, Al) were determinedby atomic absorption spectroscopy (AAS/Varian).3 Results & discussions3.1 Characterization of the spent catalystSEM image of spent catalyst containing 4.5% V, 3.5% Al,1.2% Fe and 11.8% moisture is in Fig. 1 on the left. The averageparticle size was about 1 µm. The EDX spectrum on the rightshows the metal ingredients of this catalyst. We note that bothvanadium and iron have a good scattering on the alumina-silicasupport.3.2 Sulphuric acid leachingThe leaching of spent catalyst with sulphuric acid can be rep-resented by the following equations:V2O5 + H2SO4 → (VO2)2SO4 + H2OFe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2OAl2O3 + 3H2SO4 → Al2(SO4)3 + 3H2OAccording to these equations and to the chemical composi-tion of this spent catalyst mentioned above, less than 0.25 gramsof concentrated sulphuric acid is enough for reacting with all thethree metals contained by one gram of spent catalyst. The effectof sulphuric acid concentration on leaching efficiency of valu-able metals (V, Fe, Al) was studied by varying the concentrationof the acid from 0.5 to 3 mol/l and keeping other conditionsconstant (temperature 90 ◦C, mixing time 90 min, solid/liquidratio (S/L) 5%). The results are presented on Fig. 2 where therecovery yields of metals were plotted versus concentration ofsulphuric acid. The results show that the acid concentrationof about 2.5 M is enough to dissolve about 90% of vanadium,while iron and aluminum dissolution seems to be only 60% and50%, respectively. Higher aluminum dissolution is possible byincreasing the acid concentration but vanadium and iron disso-lution tend to decrease. Moreover, higher acid concentrationin the leaching stage results in more consumption of chemicalsduring the metal separation processes and it will make leachingsolution highly viscous and difficult to filtrate.The effect of mixing time and temperature on leaching ef-Per. Pol. Chem. Eng.32 Abdulrahman Wahoud / Adel Alouche / Mohamedalkhaled Abdulbakeficiency was studied with acid concentration 2.5 mol/l andsolid/liquid ratio (S/L) 5%. The results are presented on Figs. 3and 4 which show that both of mixing time and temperature havepositive effect on leaching efficiency. It is clear that the effi-ciency increases by increasing the mixing time and temperatureand it remains constant after one hour and 80 ◦C.3.3 Sulphuric acid bakingSince direct sulphuric acid leaching was found to be inef-fective in iron and aluminum dissolution, sulphuric acid can beused more effective in metals dissolution through baking processwhich as expected converts metal oxides into soluble metal sul-fates. All backed samples were furthermore treated by leachingwith 100 ml of 2% sulfuric acid solution under fixed conditions(temperature 100 ◦C, mixing time 1 hour).3.3.1 Effect of sulphuric acid amountThe effect of sulphuric acid amount on recovery efficiency ofmetals was investigated by adding different amount of sulphuricacid (1-8 g) to 10 g of spent catalyst sample keeping other con-ditions constant (baking temperature 300 ◦C, baking time 2 h).The results are presented on Fig. 5 in the form of recovery effi-ciency of metals versus added sulphuric acid amounts. The re-sults show that four grams of acid are enough to dissolve about98% of vanadium and more than 95% and 80% of iron and alu-minum, respectively.3.3.2 Effect of baking temperatureIn order to study this effect, baking temperature was variedfrom 200 ◦C to 400 ◦C keeping other conditions constant (bak-ing time 2 h, sulphuric acid amount 5 g). The results are plottedon Fig. 6. At first, the recovery efficiency increases by increas-ing the baking temperature, but it is clear that the efficiency de-creases when the baking temperature increases above 300 ◦C.This could be possibly due to the rate of evaporation of sulfuricacid exceeding the rate of sulfation of metal oxides.3.3.3 Effect of baking durationThe effect of baking duration on recovery efficiency of metalswas investigated by baking the 10 g spent catalyst at 300 ◦Cwith four grams of concentrated sulfuric acid for different timeintervals. The results are shown in Fig. 7, which indicates thattwo hours baking time is enough for optimum metal dissolution.4 ConclusionsVanadium, iron and aluminum can be recovered from thespent catalyst with efficiency of 98 %, 95 % and 85 % respec-tively by using sulphuric acid baking followed by leaching. Theoptimum baking conditions were four grams of concentratedsulfuric acid per ten grams of spent catalyst at 300 ◦C for twohours. Sulphuric acid baking followed by leaching was foundto be the best because it consumes acid about four times less                                                                                                                                                                                                     Fig (2):The effect of sulphuric acid concentration on metal leaching yield (T =90 0C,leaching time = 90 min,S/L=5%) Fig. 2. The effect of sulphuric acid concentration on metal leaching yield (T=90 0C, leaching time = 90 min, S/L=1/10 g/ml)02550751000 30 60 90 120 150Time ( min)Y%V Fe Al Fig. 3. The effect of mixing time on leaching yield (T =90 0C, concentrationof sulphuric acid 2.5M ,S/L=1/10 g/ml )3545556575859550 60 70 80 90 100 110Temperature (0C ) Y%V Fe Al Fig. 4. The effect of temperature on leaching yield (mixing time=90 min,concentration of sulphuric acid 2.5M, S/L=1/10 g/ml)than direct sulphuric acid leaching process and it is more ef-fective in iron and aluminum dissolution. Therefore, sulphuricacid baking is expected to consume small amount of chemicalsand will generates much less waste effluents during the separa-tion process of metals with alkali solutions. Therefore, it canbe economically favorable, as well as it is accompanied muchless environmental contamination. The scale-up of baking pro-cess needs further investigation, especially with respect to thestructural material of baking device.Sulfuric acid baking and leaching of spent sulfuric acid catalyst 332011 55 10204060801001200 2 4 6 8 10g sulfuric acid/10g spent catalystY%V Fe Al Fig. 5. The effect of sulphuric acid amount on recovery yield(baking time=2 h, T = 300 0C)405060708090100100 150 200 250 300 350 400 450 Temperature (oC)Y%V Fe Al Fig. 6. The effect of baking temperature on recovery yield (baking time=2 h,sulphuric acid amount = 5 g)50607080901000 1 2 3 4 5Baking time (h)Y %V Fe Al Fig. 7. The effect of baking time on recovery yield (T=300 0C, sulphuricacid amount = 5 g)References1 Brown C M, Johnston T C, Goelz G J, C.I.M.Bulletin, 1974.2 Topose H, Clausen B S, Massoth F E, Hydrotreating catalysts-Science &Technology, Springer-Verlag, Berlin, 1996.3 Clifford R K, Spent catalyst handling, 1997.4 Chang T, Spent catalyst options, Oil Gas J. 19 (1998), 1979-1998.5 Furimsky E, Spent refinery catalysts: environment, safety and utilization,Catal. Today 30 (1996), 223-286.6 Marafi M, Stanislaus A, Spent catalyst waste management: a review part I,Resour. Conserv. Recycling 52 (2008), 859-873.7 Trimm D I, The regeneration or disposal of deactivated heterogeneous cata-lysts, Appl. Calal. A Gen. 212 (2001), 153-160.8 Marafi M, Stanislaus A, Preparation of heavy oil Hydrotreating catalystsfrom spent residue hydroprocessing catalysts, Catal. Today 130 (2008), 421-428.9 Hazardous waste management system, Vol. 68, 2003. 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