Dear Om dan Tante Forsa,

Adakah yang pernah terlibat dalam pengolahan logam/mineral dari bijih menjadi konsentrat, bahkan menjadi logam batangan yang sudah dilebur? Istilah gravity concentration dan magnetic separation adalah proses hulu yang dilakukan pada pengolahan mineral. Tapi seperti apa proses (secara mekanis) dan kontrol (secara elektrik) yang diterapkan pada sarana tersebut? Mesin apa saja yang dibutuhkan, bagaimana cara kerja dan perhitungannya? Berapa besar dana dan fasilitas yang harus dibangun?

Mohon bimbingannya,
Regards,

Proses pengolahan mineral memiliki beberapa tahapan utama seperti ore handling, size reduction and control, dan enrichment.
Nah, gravity concentration dan magnetic separation termasuk dalam proses enrichment. Mari kita bahas dari gravity concentration

GRAVITY CONCENTRATION

INTRODUCTION
Gravity methods of separation are used to treat a great variety of materials, ranging from heavy metal sulphides such as galena (sp. gr. 7.5) to coal (sp. gr. 1.3), at particle sizes in some cases below 50 microns.
These methods declined in importance in the first half of the twentieth century due to the development of the froth-flotation process, which allows the selective treatment of low-grade complex ores. They remained, however, the main concentrating
methods for iron and tungsten ores and are used extensively for treating tin ores, coal and many industrial minerals.
In recent years, many companies have re-evaluated gravity systems due to increasing costs of flotation reagents, the relative simplicity of gravity processes, and the fact that they
produce comparatively little environmental pollution. Modern gravity techniques have proved efficient for concentration of minerals having particle sizes in the 50txm range and, when coupled with improved pumping technology and instrumentation, have been incorporated in high-capacity plants
(Holland-Batt, 1998). In many cases a high proportion of the mineral in an orebody can at least be pre-concentrated effectively by cheap and ecologically acceptable gravity systems; the amount of reagents and fuel used can be cut significantly when the more expensive methods are restricted
to the processing of gravity concentrate. Gravity separation of minerals at coarser sizes as soon as liberation is achieved can also have significant advantages for later treatment stages due to decreased surface area, more efficient dewatering,
and the absence of adhering chemicals which could interfere with further processing.
Gravity techniques to recover residual valuable heavy minerals in flotation tailings are being increasingly used. Apart from current production, there are many large tailings dumps which could be excavated cheaply and processed to give high value concentrates using recently developed technology.

PRINCIPLES OF GRAVITY CONCENTRATION
Gravity concentration methods separate minerals of different specific gravity by their relative movement in response to gravity and one or more other forces, the latter often being the resistance to motion offered by a viscous fluid, such as water
or air.
It is essential for effective separation that a marked density difference exists between the mineral and the gangue. Some idea of the type of separation possible can be gained from the concentration criterion
where Dh is the specific gravity of the heavy mineral, DI is the specific gravity of the light mineral, and Df is the specific gravity of the fluid medium.
In very general terms, when the quotient is greater than 2.5, whether positive or negative, then gravity separation is relatively easy, the efficiency of separation decreasing as the value of the quotient decreases.
The motion of a particle in a fluid is dependent not only on its specific gravity, but also on its size; large particles will be affected more than smaller ones. The efficiency of gravity
processes therefore increases with particle size, and the particles should be sufficiently coarse to move in accordance with Newton's law. Particles which are so small that their movement is dominated mainly by surface friction respond relatively poorly to commercial high-capacity gravity
methods. In practice, close size control of feeds to gravity processes is required in order to reduce the size effect and make the relative motion of the particles specific gravity-dependent.

Sumber: Wills' Mineral Processing Technology, Elsevier (2005)

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