A 3D CAD rendering of the spiral circuits of the Hillendale primary wet-treatment plant. The banks of spirals are shown in green at the top of the plant, with the control room and motor control centre (both in red) on the left below the spiral banks.



The feed preparation module with its rotating trommel screen.

The first concentrate being stockpiled by the stacker.

Distributors at the top of the
spiral plant.

 Hillendale heavy-minerals plant

A primary wet-treatment plant to process mineral sands, designed by BATEMAN for Iscor Heavy Minerals (Pty) Ltd (now Ticor South Africa), has been commissioned and is operating successfully at Hillendale, close to Richards Bay in South Africa. BATEMAN, the managing contractor on the project, was responsible for the engineering design, project management and construction supervision, which were carried out under a lump-sum contract. BATEMAN was also responsible for the commissioning, which was done in terms of a reimbursable contract.

Work on this R70 million contract for Hillendale’s wet-treatment plant started in August 1997, with the design being completed by May 1998. Construction commenced in May 2000 after the finances for the project were secured. The plant was completed in April 2001. Performance guarantees in respect of the rate of solids throughput, product grade and mineral recovery were complied with.

The 1 200 t/h wet-treatment plant effectively separates gangue material in the run-of-mine ore to produce a heavy mineral concentrate, containing ilmenite, rutile and zircon, which is transported in covered trucks to the client’s central processing complex at Empangeni, about 15 km away, for further processing.

The plant is designed to be movable and comprises modules, for feed preparation, spiral separation, thickening and stockpiling the heavy mineral concentrate. These can be dismantled into components that are small enough to be transported by road to a new location when the need arises. Dismantling will be facilitated because all tanks are flanged and the structures spliced at strategic positions. The flocculant plant, motor-control centres (MCCs) and switchgear assemblies were supplied in standard containers for easy transport.

The process involves mining the heavy-mineral-bearing sand using highpressure water jets, and pumping the resulting slurry to a rotating trommel screen where the oversized waste material, mainly vegetation, is removed. The undersize material is collected in a constant-density surge tank where the slurry is densified and then diluted to a predetermined density required by the spiral circuits. In these circuits, the heavy minerals are separated from the lighter gangue utilising their difference in specific gravity. After removal of the magnetite from the spiral concentrate, using a low-intensity magnetic separator, the concentrate is pumped to a dewatering cyclone mounted at the end of the stacker and placed directly on the stockpile. From here the concentrate containing about 5 % moisture is trucked to Empangeni. Sand tailings from the spiral circuits are pumped to the dune rehabilitation area for backfill. Slimes produced by the wet-treatment plant are thickened and separated from the process water using ultra-high-rate thickeners. The supernatant liquor
from the thickeners is recycled as process water.

The plant comprises a large amount of gravity-feed piping that required careful design, particularly the spiral circuits where the material gravitates through primary, secondary and tertiary stages to separate the heavy minerals. In these circuits a considerable amount of steelwork is needed to support the HDPE (high-density polyethylene) piping which is used extensively to minimise corrosion.

The contract was awarded to BATEMAN because of its competitive bid, experience and expertise with this type of plant. The work was completed on schedule and the start-up of the plant proceeded more smoothly than is usually achieved for this type of installation. The client’s personnel expressed their satisfaction with the plant.

More details may be obtained from:

Vincent Diesel,
Project Manager - Special Projects, on +27-11-899-9111 or
email vdiesel@bmi.co.za

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