Type of screen used in carbon in Pulp CIP

An aspect very important in a plant CIP is the type of screen employed in the flow of carbon. The vibrating screens with a stainless steel square mesh is reliable, positive, works well and could be installed without any fear of malfunctioning. There are peripheral screens that include a submerged launder type of screen across the top of the carbon inter-pulp tank. Typically there might be two such launders. Each launder has two or more removable screens set in the side panels. They may be vibrated if necessary. The screens can be of 20 mesh and wedge wire with the openings in the vertical configuration. They are confident and can work with a fine grind of 80% minus 200 mesh and reduce the abrasion of the carbon and are economical as to both capital and operating costs. The design of the peripheral screen is good but there is a problem for maintenance, its accessibility.

Vibrating screens could give some problems of blinding and mainly when the activated carbon is elongated or with angular shape. The carbon has a tendency to blind the screen by getting stuck part away through the screen. But also there is a positive action, move the carbon back out of the screen opening.

Other type of screen employed is a variation of the DSM screen. This type has two DSM screens in one unit. As to blinding, sometimes there is coarse material that can blind the screen. The problem of screen abrasion is minimum but activated carbon can be abraded some times. If it soft, abrasion is high. Coconut shell carbon is not very affected by this problem.

There is a point many times that is not considered, the optimum loading of gold and silver. Loading will depend of the type of ore, cost, and metal prices. Consideration must be given to ore grade, solution values and, gold inventory and security. Lower loading can result in more frequent stripping and handling that would cause higher carbon losses and increase manpower costs.

Gold can loaded in the range 4500 to 7500 g/t. and silver loaded depends on how much silver you have along with your gold. Gold does displace silver from activated carbon white is absorption running. If silver is very important, your loading process must be consider no very interesting gold because the gold will be loaded without any problem by itself. Of course, the loading depends on the amount of gold and silver in the head solution.

The longer contact per stage, more gold will be loaded in preference to silver. T his can vary from ore to ore. A good average time would be one hour of contact per stage. It’s very much characteristic of different ores and different gangue minerals, mainly clays are a very difficult problem. Typically with a rather low grade solution, gold is loaded easily, and most the time is required five stages. Thus, if the solution has 2 ppm gold and there is a slow absorbing gangue or pulp, the circuit can be expanded to six or eight stages. There is difference in response of different ores on the rate of absorption, and can be possible build a plant with eight stages of absorption and 24 hours contact time.

In order to minimize carbon abrasion, one important design consideration is to provide for pre-abrading prior to putting carbon into the circuit. Carbon has many sharp edges that are readily worn off in the circuit and it is important to remove these edges and corners from the carbon before putting it to work. Another consideration is the method of transport of the carbon. Certainly nothing but long radius curves in ducts and piping should be installed.

Design and tip speed of mechanical agitators are very important. Plastic pipe is excellent stuff and flexible plastic pipe forms itself in very gentle bends. Friction is lower than with iron pipe. When there are clay ores, there is an effect of lubricating because they can help to suspend slurry at reasonable percent solids.