Titanium nitride in upgraded nitrided ilmenite (bulk of iron
removed) can selectively be chlorinated to produce titanium
tetrachloride. Except for iron, most other components present
during this low temperature (ca. 200°C) chlorination reaction will
not react with chlorine. It is therefore necessary to remove as much
iron as possible from the nitrided ilmenite. Hydrochloric acid
leaching is a possible process route to remove metallic iron from
nitrided ilmenite without excessive dissolution of species like
titanium nitride and calcium oxide. Calcium oxide dissolution
results in unrecoverable acid consumption. The leachability of
nitrided ilmenite in hydrochloric acid was evaluated by determining
the dissolution of species like aluminium, calcium, titanium and
magnesium in a batch leach reactor for 60 minutes at 90°C under
reflux conditions. The hydrochloric acid concentration (11%, 18%
and 25%), initial acid-to-iron mole ratio (2:1, 2.5:1 and 3.3:1), and
solid-to-liquid mass ratio (1:8.33 to 1:2.13) were varied. The results
indicate that a hydrochloric acid concentration of 25 wt% supplied
in a 2:1 acid-to-iron mole ratio would produce the most favourable
upgraded nitrided ilmenite product. The dissolution of iron in this
solution reached 97 per cent after only 60 minutes. The total
dissolution of calcium and titanium species was 0.01 and 0.11 wt%
respectively. Hydrochloric acid can therefore be used as lixiviant to
remove metallic iron from nitrided ilmenite.http://www.saimm.co.za/ai201

Heydenrych, Mike D.

Swanepoel, J.J.

Van Vuuren, D.S.

UPSpace at the University of Pretoria

TransactionPaperIntroductionThe Council for Scientific and IndustrialResearch (CSIR) in South Africa is investi-gating alternative feedstocks for theproduction of TiCl4 via low temperature (ca.200ºC) chlorination of TiN1. One of the feedmaterials considered is ilmenite (FeO.TiO2). Titanium nitride is obtained from ilmeniteby carbothermally reducing it in a nitrogenatmosphere (Reaction [1]). Reaction [1] isreferred to as the nitriding reaction. [1]The TiN can then be chlorinated at ~200ºCand ~5 bar (Reaction [2]).[2]Metallic iron chlorinates readily underthese conditions2. It is therefore required toremove the bulk of the iron from the nitridedilmenite before chlorinating the TiN. Anycomponents or impurities other than iron will,however, not react under these conditions.Table I summarizes the chemical compositionof a typical nitrided ilmenite sample.   Commercially, HCl acid is used to removeFeO, and any other metal oxides, fromthermally treated ilmenite3. The ilmenite isfirst thermally treated to ensure iron is presentas FeO during the leach reaction4. The dissolution reaction for the iron oxidepart in ilmenite is illustrated in Reaction [3].[3]The solid product obtained is known assynthetic rutile or upgraded ilmenite andcontains at least 92 per cent TiO2.Hydrochloric acid leaching is therefore apossible process route to remove iron fromnitrided ilmenite. However, the iron in nitridedilmenite is reduced to Fe during the nitridingreaction. The dissolution reaction of nitridedilmenite is therefore different from commercialprocesses in that the HCl acid will react with Feto produce H2(g), Reaction [4], instead ofreacting with FeO to produce H2O(l) (Reaction[3]).[4]Leachability of nitrided ilmenite inhydrochloric acidby J.J. Swanepoel*, D.S. van Vuuren*, and M. Heydenrych†SynopsisTitanium nitride in upgraded nitrided ilmenite (bulk of ironremoved) can selectively be chlorinated to produce titaniumtetrachloride. Except for iron, most other components presentduring this low temperature (ca. 200°C) chlorination reaction willnot react with chlorine. It is therefore necessary to remove as muchiron as possible from the nitrided ilmenite. Hydrochloric acidleaching is a possible process route to remove metallic iron fromnitrided ilmenite without excessive dissolution of species liketitanium nitride and calcium oxide. Calcium oxide dissolutionresults in unrecoverable acid consumption. The leachability ofnitrided ilmenite in hydrochloric acid was evaluated by determiningthe dissolution of species like aluminium, calcium, titanium andmagnesium in a batch leach reactor for 60 minutes at 90°C underreflux conditions. The hydrochloric acid concentration (11%, 18%and 25%), initial acid-to-iron mole ratio (2:1, 2.5:1 and 3.3:1), andsolid-to-liquid mass ratio (1:8.33 to 1:2.13) were varied. The resultsindicate that a hydrochloric acid concentration of 25 wt% suppliedin a 2:1 acid-to-iron mole ratio would produce the most favourableupgraded nitrided ilmenite product. The dissolution of iron in thissolution reached 97 per cent after only 60 minutes. The totaldissolution of calcium and titanium species was 0.01 and 0.11 wt%respectively. Hydrochloric acid can therefore be used as lixiviant toremove metallic iron from nitrided ilmenite.KeywordsTitanium nitride, upgraded nitrided ilmenite, hydrochloric acidleaching, metallic iron dissolution.* Materials Science and Manufacturing, CSIR.† Department of Chemical Engineering, University ofPretoria.© The Southern African Institute of Mining andMetallurgy, 2011. SA ISSN 0038–223X/3.00 +0.00. This paper was first presented at the, LightMetals Conference, 27–29 October 2010, MistyHills, Muldersdrift.137The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 111          MARCH 2011 ▲Leachabillity of nitrided ilmenite in hydrochloric acidThe purpose of this study was to evaluate if HCl acid canbe used as lixiviant to remove Fe from nitrided ilmenitewithout excessive product (TiN) dissolution and dissolutionof components that could lead to unrecoverable acidconsumption (e.g. CaO forming CaCl2).The leachability of Fe, Al, Ca, Mg and Ti from nitridedilmenite was evaluated by investigating different acid concen-trations, initial HCl-to-Fe mole ratios, and solid-to-liquidmass ratios at a fixed period where Fe dissolution is virtuallycomplete.ExperimentalSample characteristicsNitrided ilmenite was obtained by nitriding unroastedHillendale ilmenite at approximately 1325 °C with 30 per centexcess bituminous coal under N2(g) for 6 hours. The nitridedilmenite was cooled down under N2(g) and then magneticallyseparated from the residual char. Chemical analysis (ICP-OES) was conducted on the nitrided ilmenite sample todetermine its composition. Table I presents a composition forthe nitrided ilmenite sample obtained. The results in Table I (average of three samples) werenormalized to include the conversion of TiO2 to TiN. Thisconversion (~90 per cent) was estimated based on mass lossof sample during the nitriding reaction. This estimation isbased on the assumption that all the iron oxide present in theilmenite sample reduces to Fe during the nitriding reaction. Particle size distribution analysis of the nitrided ilmenitesample found its mass mean particle diameter equal to 185 μm.Experimental procedureAcid leaching of nitrided ilmenite was carried out using a 500ml three-necked glass flask as reactor. The reaction vesselwas equipped with two condensers in series and an overheadstirrer fitted with a PTFE-coated shaft and impeller. Atemperature controlled heating mantle regulated temperatureinside the reaction vessel. The required mass of nitrided ilmenite sample (d50 = 185 μm) was first loaded into the reaction vessel. Once thereactor and solids reached a temperature of 90°C, HCl acid(analytical grade) with the required concentration (11%, 18%or 25%) was added to the reactor at a rate of 10 ml/min froma second heated vessel. The 100 ml HCl acid was thus addedover 10 minutes. This was done to prevent excessive foamingcaused by H2(g) evolution. A stirring speed of 100 rpm wasapplied to keep the slurry suspended during the leachingexperiment.After the required reaction period (60 minutes), the slurrywas filtered off and the solid residue thoroughly washed withhot water. The washed solids were then heated in air for 60minutes at 80°C. Chemical analysis on both leached solids(ICP-OES) and leach liquor (ICP-AES) were conducted todetermine the solids’ chemical composition and the total Ti,Ca, Mg and Al in the leach liquor. Results and discussionThe extent of Fe dissolution after 60 minutes The weight per cent Fe dissolved after 60 minutes in 90°C HClacid is summarized in Table II. The results are reported forthree HCl acid concentrations at three different initial HCl/Femole ratios. The weight per cent Fe dissolved was calculatedfrom the results for the leached solid’s chemical analysis.The results summarized in Table II indicate that thedissolution of Fe can reach levels of at least 96 per cent after60 minutes in 90°C HCl acid. The dissolution of Fe istherefore virtually complete after 60 minutes. A leachduration of 60 minutes is therefore assumed sufficient toevaluate the dissolution of other components in HCl acid.The time required to obtain the same FeO dissolution inReaction [3] is approximately 3–5 hours4–6. The residencetime required for Fe dissolution is therefore significantly lessthan that of partially reduced iron (i.e. iron as FeO).Effect of HCl concentration Figure 1 illustrates the effect of HCl acid concentration on thedissolution of Al, Ti, Ca and Mg. An increase in HCl acidconcentration results in an increase of Al and Ti dissolutionbut a decrease in the dissolution of Ca and Mg. The increasein Ti dissolution with an increase in HCl acid concentration iscomparable with previous findings5,7.The dissolution of components illustrated in Figure 1 isrelatively low. These components will therefore still bepresent in the upgraded nitrided ilmenite. This is acceptablefor the low temperature chlorination process as these species▲138 MARCH 2011        VOLUME 111  The Journal of The Southern African Institute of Mining and MetallurgyTable IChemical composition of nitrided ilmeniteComponent Normalized mass %SiO2 3.52Al2O3 1.87Fe(metal) 45.32TiO2 5.43TiN 37.87CaO 0.13MgO 0.62K2O 0.03MnO 1.26P2O5 0.05V2O5 0.28C(total) 3.38S(total) 0.21Table IIIron dissolution in hydrochloric acid after 60 minutesHCl concentration (wt%) NHCl/ NFe (mol/mol) Fe dissolved (wt%)11% 2.0 96.82.5 97.23.3 97.718% 2.0 96.92.5 97.93.3 97.225% 2.0 96.82.5 97.23.3 96.6will not react with Cl2 (as discussed earlier). The dissolutionof these species (excluding Ti), and other impurities, isalmost complete in existing FeO-leach practices4,6. Effect of initial HCl/Fe mol ratioTable III summarizes the results obtained from the evaluationof different HCl acid-to-iron mole ratios on the dissolution ofAl, Ti, Ca and Mg in 25 wt% HCl acid. The weight per centdissolved is based on the results of the leach liquor analysis.The tendency for Ti dissolution to increase with anincrease in the acid-to-iron mole ratio, as reported in Table III, is similar to findings from previous work7–9. Theextent of Ti dissolution is, however, significantly less due tothe high acid-to-ilmenite ratios evaluated in these previousworks. For example, after 8 hours in a 105°C 6M HCl acidsolution, van Dyk et al.8 found that 45 per cent Ti dissolvedin a 60:1 acid-to-ilmenite ratio, and approximately 5 per centin a 4:1 acid-to-ilmenite ratio. The dissolution of all species given in Table III signifi-cantly increased with an increase in acid-to-iron mole ratio.The dissolution of Al increased with 67 per cent whenincreasing the acid-to-iron ratio from the stoichiometric levelof 2:1 to that of 3.3:1. The dissolution of Ti, Ca and Mgincreased significantly more, with increases of at least 4 times more. The dissolution of these species is thereforedependent on the amount of excess (or free) acid availablefor reaction. The optimum mol ratio of acid-to-iron would beat levels equal to or very close to the stoichiometric ratio.Effect of solid-to-liquid mass ratio Figures 2 and 3 illustrate the effect of solid-to-liquid massratio on the dissolution of Ca and Ti respectively. Magnesiumpresents the same dissolution profile as illustrated in Figure 2, and Al the same dissolution profile as illustrated inFigure 3.The results illustrated in Figure 2 indicate that thedissolution of Ca (and Mg) is significantly more favourable atlower solid-liquid mass ratios than at higher ratios. Thissuggests that the dissolution of Ca and Mg is dependent onthe solid-liquid mass ratio of the reaction solution. The dissolution of Ti and Al seems to not be stronglydependent on the solid-liquid mass ratio in Figure 3. Theresults do, however, suggest that the acid-to-iron mol ratiohas a dominant effect on the dissolution of Ti and Al.Optimum HCl leach conditionsThe optimum HCl leach conditions would be where the HClacid can dissolve virtually all of the Fe from the nitridedLeachabillity of nitrided ilmenite in hydrochloric acidTransactionPaper139The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 111          MARCH 2011 ▲Figure 1—Effect of hydrochloric acid concentration on dissolution(90°C, d50 = 185 µm, 100 rpm, 2.5 mol HCl/mol Fe)Table IIIThe effect of initial HCl/Fe mol ratios on dissolutionin 25% HClExcess acid (mol %) 0 20 40NHCl/ NFe (mol/mol) 2.0 2.5 3.3Al 2.14 2.99 3.57wt% Ca 0.01 0.03 0.05dissolved Mg 0.17 0.49 0.84Ti 0.11 0.27 0.44Figure 2—Effect of solid/liquid mass ratio on calcium dissolution (90°C,d50 = 185 µm, 100 rpm)Figure 3—Effect of solid/liquid mass ratio on titanium dissolution (90°C,d50 = 185 µm, 100 rpm)Leachabillity of nitrided ilmenite in hydrochloric acidilmenite but with little dissolution of other species, especiallyCa (unrecoverable acid consumption) and Ti (part ofproduct). The HCl acid with highest concentration conformingto the above considerations would be the selected acidconcentration.The findings from this study indicates that a 25 wt% HClacid with a 2:1 acid-to-Fe mole ratio at 90°C would produceupgraded nitrided ilmenite closest to the required conditionsas described above.The normalized composition for a nitrided ilmenitesample leached with 25 wt% HCl acid for 60 minutes (ca.90°C) is given in Table IV for an acid-to-Fe mole ratio of 2:1.The limited dissolution of CaO, as illustrated in Table IV,will lead to reduced acid consumption compared to that ofFeO-leach units where most of the CaO is dissolved4. Acidlosses can be attributed to dissolved CaCl26.Low temperature chlorination of the product summarizedin Table IV will result in 0.051 mole unwanted Cl2consumption for each mole TiCl4 produced. Only Fe will reactto produce unwanted FeCl31. This translates to a 97.8 percent yield (moles reactant required to produce desired product(TiCl4) divided by moles reactant (Cl2) fed) for Cl2 supplied tothe low temperature chlorination reactor. The remainingsolids will leave the reactor as inert material. These inertmaterials can be treated and partially recycled back to thenitriding unit to recover some of the unreacted TiO2. The TiO2 and FeO content in slag used for the high-temperature chlorination process are typically 85 and 12 wt% respectively10. If only FeO contributed to unwantedCl2 consumption (FeCl2 produced), a 92.7 per cent yield forCl2 supplied can be obtained in the chlorination reactor.Chlorine losses more than three times higher can therefore beexpected in the conventional chloride process compared to thelow temperature chlorination process.ConclusionsThe results obtained from this study indicate that HCl acidcan be successfully used as lixiviant to remove Fe fromnitrided ilmenite. The following is a summary of findings from this study:➤ Metallic iron dissolution from nitrided ilmenite reachedlevels of at least 96 per cent after 60 minutes in 90°CHCl acid. This is applicable for all HCl acid concen-trations (11%, 18% and 25%) evaluated in this study. ➤ An increase in HCl acid concentration results in anincrease of Ti and Al dissolution, and a slight decreasein Ca and Mg dissolution.➤ The dissolution of all four species (Al, Ca, Mg, and Ti)increased with an increase in excess acid available forreaction. The excess acid available for reaction (or acid-to-iron mole ratio) had the largest effect on thedissolution of Al and Ti.➤ The dissolution of Ca and Mg reduced for an increase inthe initial solid-to-liquid mass ratio, but the dissolutionof Al and Ti was not strongly dependent on the solid-to-liquid mass ratio. The solid-to-liquid mass ratio ofthe reaction solution had the largest effect on thedissolution of Ca and Mg.AcknowledgementsThe authors express their gratitude to The Department ofScience and Technology for funding the research.References1. MOSTERT, G.J. et al. Process for the recovery of titanium values. U.S. Pat5,224,986: 6 July 1993. 2. VAN VUUREN, D.S. and STONE, A.K. Selective recovery of titanium dioxidefrom low grade sources, South African Chemical Engineering Congress,20–22 September 2006, Durban.3. LANYON, M.R., LWIN, T., and MERRITT, R.R. The dissolution of iron in thehydrochloric acid leach of an ilmenite concentrate. Hydrometallurgy, vol. 51, no. 3, 1999, pp. 299–323. 4. WALPOLE, E.A. and WINTER, J.D. The Austpac ERMS and EARS Processesfor the Manufacture of High-Grade Synthetic Rutile by the HydrochloricAcid Leaching of Ilmenite, Chloride Metallurgy 2002—InternationalConference on the Practice and Theory of Chloride/Metal interaction,October 2002, Montreal. 5. WANG, Z., XUE, J., WANG, H., and JIANG, X. Kinetic study of hydrochloricacid leaching process of ilmenite for rutile synthesis, EPD Congress 2009,The Minerals, Metals & Materials Society, 2009, pp. 837–843. 6. WINTER, J. Production of Synthetic Rutile by Continuous Leaching. U.S. Pat7,404,937: 29 July 2008. 7. EL-HAZEK, N., LASHEEN, T.A., EL-SHEIKH, R., and ZAKI, S.A.Hydrometallurgical criteria for TiO2 leaching from Rosetta ilmenite byhydrochloric acid. Hydrometallurgy, vol. 87, 2007, pp. 45–50. 8. VAN DYK, J.P., VEGTER, N.M., and PISTORIUS, P.C. Kinetics of ilmenitedissolution in hydrochloric acid. Hydrometallurgy, vol. 65, 2002, pp. 31–36. 9. MAHMOUD, M.H.H., AFIFI, A.A.I., and IBRAHIM, I.A. Reductive leaching ofilmenite ore in hydrochloric acid for preparation of synthetic rutile.Hydrometallurgy, vol. 73, no.s 1–2, 2004, pp. 99–109. 10. PISTORIUS, P.C. Ilmenite smelting: The basics. The Journal of SouthernAfrican Institute of Mining and Metallurgy, vol. 108, 2008, pp. 35–43.  ◆▲140 MARCH 2011        VOLUME 111  The Journal of The Southern African Institute of Mining and MetallurgyTable IVChemical composition of leached nitrided ilmeniteComponent Normalized mass %SiO2 6.06Al2O3 3.56Fe(metal) 2.15TiO2 10.00TiN 69.90CaO 0.12MgO 1.29K2O 0.07MnO 1.10P2O5 0.03V2O5 0.56C(total) 5.16S(total) 0.27

Leachability of nitrided ilmenite in hydrochloric acid

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Leachability of nitrided ilmenite in hydrochloric acid

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