Feasibility of fluxless smelting of titaniferous magnetite ore in a pilot-plant open-arc DC furnace

Geldenhuys, Isabella Johanna (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Titaniferous magnetite (titanomagnetite) is nominally defined as magnetite deposits containing more than one mass percent of titanium dioxide (TiO2). Titanomagnetite deposits are known for being difficult to process; this is primarily due to the complex nature of the mineral compounds that make up the ore. The complex mineralisation means chemical upgrading processes are needed to derive economic value from the ore. While titanomagnetite deposits are widely processed for the recovery of vanadium, or vanadium and iron, titanium is not commercially recovered. The current study reviews the feasibility to extract iron and vanadium while producing a high-titanium slag via fluxless smelting in an open-arc direct current (DC) furnace. The study evaluated the technical feasibility via a pilot-scale study and furthermore considered the viability of the titania-rich furnace slag produced during the study, as a potential feedstock for the production of pigment and metal. Fluxless smelting could offer an opportunity to unlock all three valuable commodities from South Africa’s Bushveld Complex, the largest known deposit of its kind in the world. The demise of Highveld Steel and Vanadium has created an opportunity to implement the best available technology for this complex ore, leveraging the know-how and experiences of the ilmenite smelting industry in South Africa. A pilot-scale DC furnace was operated continuously for 17 days at power levels of up to 1.3 MW. During the smelting test, 108 tons of titaniferous magnetite concentrate was processed. Smelting of the concentrate involved a simple recipe which comprised of concentrate and low-ash anthracite fed to the furnace in the desired proportion to achieve the targeted metallurgical result, namely an undiluted titania-rich slag and a vanadium-bearing iron product. The test demonstrated that slag composition by virtue of the degree of reduction could be optimised for the desired specification, namely slag containing at least 85% TiO2. Due to the nature of open-arc smelting, the furnace can be operated to optimise metallurgy and is not constrained with respect to the operating power. Slag containing 89% TiO2 was consistently produced demonstrating the production of high-grade titania slag in the absence of fluxes. Phase chemically the slags were found to be dominated by the presence of an M3O5 phase (where M = Fe, Ti, Mg, Al and Mn), which is also typical of high-titania slags produced from the smelting of ilmenite. The compositional invariance observed for industrial ilmenite slags was established to also apply to the slags produced during the current study. Slags produced from titaniferous magnetite deposits will compete with higher grade titania feedstocks. The fact that the slags produced during the study resembled industrial slags is encouraging. A flowsheet was developed based on the outcomes from the pilot test, namely a mass and energy balance for fluxless smelting of titaniferous magnetite in a DC furnace. A detailed benchmarking study would be required to assess the economic viability in a highly competitive market. The results from the study supported the premise that the comprehensive processing of vanadium-bearing titaniferous magnetite deposits is technically feasible. The outcomes provide valuable insights into the behaviour of a fluxless titaniferous magnetite smelting process, presents a foundation for future work, and improves the general understanding of the requirements, challenges and benefits of fluxless smelting of titanomagnetite ores.

AFRIKAANSE OPSOMMING: Titaanhoudende magnetiet (titanomagnetiet) word nominaal gedefinieer as magnetietdepositos wat meer as een massa persent van titaniumdioksied (TiO2) bevat. Titanomagnetietdepositos is bekend om moeilik te wees om te prosesseer; dis hoofsaaklik as gevolg van die komplekse aard van die mineraalsamestellings waaruit die erts bestaan. Die komplekse mineralisasie beteken chemiese opgraderingprosesse word benodig om ekonomiese waarde uit die erts te verkry. Terwyl titanomagnetietdepositos algemeen geprosesseer word vir die herwinning van vanadium, of vanadium en yster, is titanium nog nie kommersieel herwin nie. Die huidige studie beoordeel die uitvoerbaarheid daarvan om yster en vanadium te ekstraheer terwyl ’n hoë titaniumslak via flukslose smelting in ’n oopboog direkte stroom (DC) oond geproduseer word. Die studie evalueer die tegniese uitvoerbaarheid via ’n loodsskaalstudie en het verder die lewensvatbaarheid van die titaniumryke oondslak geproduseer deur die studie oorweeg as ’n potensiële voermateriaal vir die produksie van pigment en metaal. Flukslose smelting kan ’n geleentheid skep om al drie waardevolle kommoditeite uit Suid-Afrika se Bosveld Kompleks te ontsluit, die grootste bekende deposito van sy soort in die wêreld. Die ondergang van Highveld Steel and Vanadium het ’n geleentheid geskep om die beste beskikbare tegnologie vir hierdie komplekse erts te implementeer, wat die kennis en ondervinding van die ilmenietsmeltingindustrie in Suid-Afrika gebruik. ’n Loodsskaal DC-oond is aaneenlopend vir 17 dae by kragvlakke van tot en met 1.3 MW bedryf. Tydens die smeltingtoets is 108 ton titaanhoudende magnetietkonsentraat geprosseseer. Smelting van die konsentraat het ’n eenvoudiger resep behels wat bestaan het uit konsentraat en lae-as antrasiet in die oonde gevoer in die gewenste proporsie om die doelwit metallurgiese resultaat te kry, naamlik ’n onverdunde titania-ryke slak en ’n vanadiumdraende yster produk. Die toets het gedemonstreer dat slakkomposisie op grond van die grade van reduksie geoptimeer kan word vir die gewenste spesifikasie, naamlik slak wat ten minste 85% TiO2 bevat. As gevolg van die aard van oopboogsmelting, kan die oond bedryf word om metallurgie te optimeer en is nie beperk ten opsigte van die bedryfskrag nie. Slak wat 89% TiO2 bevat, is konstant geproduseer wat die produksie van hoë-graad titaniaslak in die afwesigheid van flukse demonstreer. Fase chemies is die slak gevind om gedomineer te wees deur die teenwoordigheid van ’n M3O5- fase (waar M = Fe, Ti, Mg, Al en Mn), wat ook tipies is van hoë titaniaslakke geproduseer uit die smelting van ilmeniet. Die komposisionele onveranderlike waargeneem vir industriële ilmenietslakke is vasgestel om ook op die slakke geproduseer in die huidige studie, toepaslik te wees. Slakke geproduseer uit titaanhoudende magnetietdepositos sal kompeteer met hoër graad titaniavoermateriaal. Die feit dat die slakke geproduseer in die studie aard na die industriële slakke, is bemoedigend. ’n Vloeidiagram is ontwikkel gebaseer op die uitkomste van hierdie loodstoets, naamlik ’n massa- en energiebalans vir flukslose smelting van titaanhoudende magnetiet in ’n DC-oond. ’n Gedetaileerde normstudie word benodig om die ekonomiese lewensvatbaarheid in ’n hoogs kompeterende mark te assesseer. Die resultate van die studie ondersteun die veronderstelling dat die omvattende prosessering van vanadiumhoudende titaanhoudende magenetietdepositos tegnies uitvoerbaar is. Die uitkomstes lewer waardevolle insig in die gedrag van ’n flukslose titaanhoudende magnetietsmeltingsproses, lewer ’n fondasie vir toekomstige werk, en verbeter die algemene verstaan van die vereistes, uitdagings en voordele van flukslose smelting van titanomagnetietertse.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108177
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