Mining & Trade News

Abstract:

Ilmenite and rutile are a source of titanium pigment and titanium metal. These minerals exist as saprolite metamorphic rocks, placer deposits in alluvial environments and beaches and as float or pods and veins in basement anorthosite. These minerals have potential to transform the economy of Malawi through mining and processing to value added products.  

1.0 Ilmenite and Rutile

Ilmenite is a mineral composed of titanium dioxide and iron (FeTiO3) while Rutile is made up of titanium dioxide (TiO2). These minerals occur in igneous and metamorphic rocks. They are a primary source of titanium dioxide pigment mainly used in the production of paints, plastics, paper products and for formulating sunscreens that block harmful UV rays.  

Most ilmenite in Malawi accumulates as heavy mineral sands during stream transport and wave action along lake beaches. Ilmenite can be converted into pigment grade or synthetic rutile via either sulfate process or chloride process. Ilmenite can also be smelted to produce liquid iron and a titanium-rich slag. Rutile often appears as small needles quartz and gem stones giving asterism or cat’s eye effect. The high dispersion of rutile allows it to break up white light into multi-colored points, further enhancing its optical allure.

2.0 Occurrence

Rutile is commonly found in igneous and metamorphic rocks, often alongside other minerals such as quartz and feldspar.   . It often appears in varying reddish to brownish translucent colours.  

The paragneiss of Kasiya area hosts a weathering profile of rutile mineralisation in extensive, shallow, blanket-like formations popularly known as saprolite.  

The Kasiya rutile project will use hydro mining technic and the slurry material from the pits will undergo processing at the wet plant where the cyclones and up-current classifiers will be employed to eliminate fine particles smaller than 45µm. The heavy mineral concentrate (HMC) will be isolated using both coarse and fine spiral circuits to produce coarse and fine gravity tailings enriched with graphite. The graphite will be recovered through combined gravity separation of tailings using froth flotation, which will include polishing and the use of stirred media mills.

Tengani rutile/ilmenite project in Nsanje contains a combination of rutile and ilmenite with ilmenite in great abundance. The rutile/ilmenite deposit exist in form of place deposit derived from adjacent anorthositic rocks and as an ore in the Basement Complex anorthositic rocks.   In the basement anorthositic rock, the ilmenite appears to exist in an intergrowth with rutile, surrounded by very abundant strongly fractured reddish-brown almandine garnet (Viv Stuart Willams, 2021). This is a common occurrence of the alluvial rutile/ilmenite deposit within the alluvial plain. Further research is required into less cost production of TiO2 product.

Makanjira Heavy Mineral Sands is a weathered eluvial layer of Precambrian gneiss containing garnet hornblende biotite. The beach placer is a loose yellow medium sand containing titanium– zirconium. Its particle size varies from 0.1 to 0.5 mm. Ilmenite and zirconite are the main constituents occurring in 0.07 - 0.30 mm size fraction and 0.07 - 0.18 mm size fraction respectively. The mud content has an average value of 0.89%. The ilmenite will be recovered through a combination of gravity, magnetic and electric separation. Lake Chilwa Heavy Mineral Sands consist of beach and dune deposits that were deposited and preserved through several cycles of lake level fluctuations.  

The main HM deposits are located on a very distinct strandline where the conditions of sediment supply, lake level, and hydrological were favourable for the formation and preservation of the sand deposits.  

Sediments, including HMs, were eroded and supplied by several streams and rivers flowing into the lake from surrounding basement gneiss and alkaline intrusion complexes.  

The HM characteristics of each deposit are determined by the proven rock types. Some deposits have local point sources contributing to the HM assemblage.

3.0 Uses of Ilmenite and Rutile

Titanium is critical for industries like aerospace, defense, and renewables. Due to its semiconductor properties, smaller wavelength (<400 nm), high refractive indices, high birefringence and high dispeion make it a raw material for production of certain critical optical elements. Titanium dioxide can be used as a cellulose that covers welding electrodes.   When converted into a metal it is used in aerospace, automotive, electronics industries, and medical devices.  

4.0 Resource Estimate

Sovereign Metals has come up with a mineral resource of broad and contiguous zones of highgrade rutile and graphite across a very large area of over 201km2 within a 15-meter depth of saprolite material. A resource of 17.0 million tonnes of rutile was estimated to exist. The ore contains an average grade of 1.0% rutile. Makanjira Heavy Mineral Sands consist mainly of ilmenite and zirconite with the ore body floor composing a weathered eluvial layer of Precambrian gneiss containing garnet hornblende biotite. The Makanjila titanium-zirconium placers consist of a reserve totaling 367.5869 million tons of which Ilmenite is 9763.676 thousand tons (average grade 42.39kg/m3).  

Crown Minerals estimates that the Tengani EPL contains 1.6 million tonnes of rutile. Most of the rutile is inter twinned with 7.2 million tonnes of ilmenite which calls for the use of Ortech Technology to take the titanium into solution and then recover Ti from the solutions. .  

The Nkhotakota- Augustino stretch along the western shore of Lake Malawi contains an inferred resource of 18.0 million tonnes at 3.7% ilmenite.  

Crown Minerals Ltd has observed pods and thin veins as a common type of mineralization in the anorthosite body. This is the main source of alluvial and eluvial ilmenite/rutile at Tengani.  

The Lake Chilwa beach placer is proving to have a large deposit of ilmenite. Chilwa Minerals has come up with an Inferred Resource of 61.6Mt at 3.9 % THM.  

A recent investigation by Crown Minerals on the basement anorthosite has shown that it hosts abundant titanium mineralization in the basal units of the complex. This mineralization has been observed in an area of 11 Km2. An inferred resource of 3.3 Mt has been estimated using a density of 1 Kg/m3 within a depth of 0.3 m. More work is required to prove that this can be another world class deposit of titanium mineralisation.  

5.0 Value addition

High-temperature chemical reaction is required to transform ilmenite and rutile into titanium dioxide (TiO2). Coal and chlorine gas are used in a fluidized bed to transform ilmenite and rutile into TiO2. Regulated high-temperature of about 1000 0C is used to turn titanium ore and chlorine gas into titanium tetrachloride, known as TiCl4. Hydrolysis and Oxidation turns TiCl4 into TiO2.  

Malawi has the potential to smelt ilmenite and rutile to form titanium oxide slag and pig iron. The titanium slag or pig iron can be converted into titanium pigment using chloride process in combination with salt and cheap power.  

Titanium metal is produced through the Kroll process, where it's reduced with magnesium.  

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