Ilmenite-haematite

Anorthositic deposits - nearly all of the known commercially important rock deposits of titanium minerals are associated with anorthositic or gabbroic rocks. There are three main types (a) ilmenite-magnetite (titanoferous magnetite), (b) ilmenite-haematite, and (c) ilmenite-rutile. 

The ilmenite-haematite deposits usually contain these minerals in intimate intergrowths, and hemo-ilmenite concentrates can be produced from these ores. 

The resultant slag, a complex mixture of titanates, may contain 70—85% Ti02- The slag route is particularly useful when ilmenite is closely associated with haematite, from which it cannot economically be separated mechanically. Because the iron content of the slag is low, its use reduces the quantity of iron sulfate in the Hquid effluent of sulfate process plants. Slag used as a feedstock for TiCl production must be low in magnesium and calcium. A variety of other ilmenite beneficiation or synthetic mtile processes have been pursued, primarily to provide alternative chloride process feedstocks. Low grade ilmenite... 

When the A ion in an ABX3 compound is too small to form the perovskite structure, say when its radius is less than about i-o A, the alternative ilmenite arrangement sometimes occurs. This structure is closely related to that of corundum and haematite ( 8.46) and may be described as an hexagonal close-packed array of X ions (usually oxygen ions) with A and B ions each occupying one-third of the octahedrally co-ordinated interstices. Thus both A and B ions are now 6-co-ordinated by anion neighbours. 

Samples of rock matrix from between fractures, comprised mainly of tuffs and ignim-brites (Michie 1996). These are the most volumetrically important rock types within the BVG. Access of radionuclides to the rock matrix is achieved by diffusion (Lever Bradbury 1985). Sorption of the radionuclides on pore surfaces in the rock matrix provides substantial retardation for the radionuclides (Nirex 1995). These rocks have a silicate-dominated mineralogy quartz, chlorite, feldspar with minor ilmenite and secondary haematite and carbonate minerals. 

---