Multotec spirals were developed some years ago. Basically, the spirals are of fiberglass construction, with a hard wearing polyurethane coating and were designed as a two-stage unit with the upper primarily section on the same central shaft as the lower middlings retreatment section. This arrangement considerably simplifies plant layout and minimize ancillary equipment. The separation of coal and heavy minerals from gangue in spirals is a gravity separation process based on the action of centrifugal force on slurry.
It is important to indicate that this spiral process has more advantages over the other minerals separation processes in that they do not have any moving parts and the addition of chemical reagents is not required to operate the equipment. Essentially, development of the Multotec spiral range started with a basic coal spiral which led to the development of the 1m diameter high capacity coal spiral. This equipment features an auto reject channel that overcomes the problem of beaching due to oversize particles in the feed whilst offering improved removal of high density particles. In fact, the increased fluidity generated around the centre column increases slime removal.
A new unit, the MX 7 high capacity spiral concentrator incorporates two stages of concentration in a single unit. This characteristic has resulted in a substantial reduction in costs and building size when compared with two completely separate stages of concentration. The advantages of the auto reject channel are included in the Multotec heavy mineral spiral. These spirals and accessories are designed to operate under extreme abrasion conditions and together with their distributors and housing framework are extremely friendly. Several profiles are available in either single, twin or triple start units with three, five or seven turns. Several trough angles are available to suit metallurgical requirements. Ancillary equipment such as distributors, modular piping and launders are also supplied.