Modern Mining April 2019

MINERAL SANDS

approximately 1,5 m and, when dry, the clay will be about 0,4 m thick. Landform reconstruction and topsoil return forms an important part of the process. The des- iccated fine tails are worked by dozer into the coarse tails to make a nominal 2 m thick water retention layer at the surface, graded into final landform and topsoil replaced on top via front- end loader, dump truck and dozer or grader. Then the area will be ready for rehabilitation. Two stages of mining and development are envisaged. Stage 1 (0-3,5 years) will comprise a single DMU feeding the initial wet concentrator plant (WCP1) at 1 750 t/h, or 13 Mt/a. During Stage 1 high grades averaging 9,1 % HM will be mined. The existing Kwale Operations DMU built by Piacentini, which is now redundant, will be refurbished and relocated to Toliara for Stage 1 operations. Stage 2 (3,5-32,5 years) will see the addition of a second DMU (DMU2) and WCP (WCP2) operating at 825 t/h. The combined mining rate will be 2 475 t/h or 19 Mt/a, with the total D11 fleet consisting of four machines. The aver- age grade will be 6,4 % HM. The increase to a 19 Mt/a mining rate is subject to obtaining appropriate environmental permitting. The flowsheet developed for the wet con- centrator plants is a simple three-stage spiral circuit and produces a total mineral concen- trate grade >90 %. Each WCP will incorporate a de-sliming cyclone and thickening circuit designed for a wide range of ore clay content. Triple start MG12 spirals were selected for the rougher (2,5 tonnes per start) and scaven- ger (2,3 tonnes per start) duties. This combines two traditional separation stages into a single stage which reduces pumping and plant foot- print (reducing capex as well as opex). The cleaner spirals are twin start VHG. The design incorporates a constant density surge tank that will provide a one-hour buffer between DMU and WCP. WCP1 is designed with some modular ele- ments to facilitate relocation in future years (11, 19 and 29). Ilmenite, rutile and zircon final products will be produced at the 140 t/h Mineral Separation Plant (MSP). Mineral recoveries of 93,9 % ilmenite, 79,0 % zircon and 73,7 % rutile are expected. The average annual production (excluding the first and last partial operating years) will be 806 kt of ilmenite (sulphate, slag and chloride), 54 kt of zircon and 8 kt of rutile. A tall building (approximately 50 m) design with multiple machine floors to reduce operat- ing cost (reduced materials handling equipment and drives) has been adopted for the MSP.

(approximately 400 mm screen), passes up the DMU conveyor which discharges to a slurry area where water is added, and then screened at 4 mm. The screen undersize is pumped to the wet concentrator plant (WCP). Oversize is disposed of in the pit void. Quartz sand separated by the WCP con- stitutes the coarse tailings and is pumped, initially to an out-of-pit storage facility and later to the mining pit void where a move- able tails stacker de-waters the slurry. Water is recovered and pumped back to the WCP and is stacked to a height approximating the planned finished level, and worked by dozer into fine tails evaporation ponds. Flocculated clay tailings (fine tailings) from the thickener at the WCP are pumped to evap- oration ponds built on coarse tails. Initially, until enough coarse tails area is available, some ponds will be constructed on ore and the dried tails removed to allow mining later on. The tails ponds will be filled to a depth of

Layout of the Toliara project.

24  MODERN MINING  April 2019