A gold gravity concentrate is usually upgraded using a shaking table and many designers ignore how to clean the concentrate obtained in the gravity circuit. It is important to mention that the primary gold concentrate may be a high or low grade product. In the first case the gold content is usually 1,000-1,200 g/t, and in the second case the gold is present in quantities as high as 25,000 g/t of gold. The objective of the cleaning stage is to eliminate impurities and increase the gold content in order to get a material, which may be melted to produce a gold bar. The cleaning circuit may include one or two stages depending on the initial gold grade. It is common to obtain gold concentrates containing more than 50% of gold.
The cleaning circuit is equipped with shaking tables such as Deister or Wilfley model. The last years the introduction of the Gemini table created a new perspective in the design of gold gravity circuits. The first two models have been used for a long time. Some designers are oriented to use a Gemini table due to offers a good metallurgical performance and its operation is not complex. Nevertheless, the main restriction is related to its processing capacity, which is influenced by the feed gold grade. It means, low grade material is processed slowly than high grade concentrates. Some designs include a bin that feeds the Gemini table and the balance is returned to the bin. Other designs consider the installation of centrifugal concentrators as pre-cleaning units. In the second case the gold content is upgraded from 250-300 oz/t to 3,000-3,500 oz /t with gold recoveries as high as 90%.
When other centrifugal unit is required in the cleaning circuit, a magnetic concentrator unit may be included in order to separate precious metals from magnetic material (e.g. magnetic, metallic iron). It is important to mention that when a magnetic concentrate is included after a centrifugal unit, this unit is installed on the table to remove iron compounds and update the table concentrate grade. When the design is sophisticated, the magnetic are directed with the low density gangue in the table tails. The design is good, but some gold particles are trapped and collected in the magnetic concentrate. In some cases the magnetic concentrate has reported 40 oz/t of gold. For this reason many designers prefer to perform magnetic concentration first and the magnetic concentrate is treated by intensive cyanidation. Other important consideration of the shaking table is related to the gold losses in the table tails. In this case this stream must be recycled to the prior cleaning stage or appropriate point such as the grinding circuit. Essentially, a careful study of the design must consider all the possible options. Probably, to recycle the table tails to the first cleaning unit is a good option, more even if a centrifugal unit has been installed to recover and improve the gold grade.
Shaking table may be used to clean gold gravity concentrates