Contract installation services


Heap leach pads

The heap-leach process is now a globally accepted means of large–scale surface mining and extraction employing the use of chemical reagents to percolate through stacks or heaps of generally low grade crushed oxide mineral deposits in the generation of highly charged chemical solutions which are further processed in the winning of valuable non-ferrous metals on a large commercial scale and which generally include gold, copper and nickel.

The techniques employed in heap leaching require an approach to mineral extraction which constitutes a fine balance between commercial and environmental expedients. The client requires the maximum extraction efficiencies at minimal cost and with minimal loss of product whilst the environmental councils insist that there should be minimal negative impact on the local environment.

The use of flexible geomembrane liners in this process is crucial in that the liner should be resistant to the chemically charged solutions passing over and stored within them, whilst the installation techniques should ensure that the liner system remains intact and does not allow the leakage or loss or valuable product.

The liner system occupies a position at the base of each heap pad or stack and collects and diverts product in solution away from the pad into solution trenches down to a series of ponds or lagoons where pregnant solution is stored and further processed.

The entire process is a closed loop or circuit and operates entirely under the effects of gravity.

Tailings and slimes dams

In comparison to the heap leach process, these tailings and slimes dams are large scale waste deposits from the mining or process industries which contain very fine, silt grade fractions of product which are transported by pipelines to the waste dam or dump and then discharged in hydraulic form over the floor and walls of the dam in a series of walls and beaches consolidating before the next phase of discharge is made.

These dams and dumps are typical of waste areas adjacent to fertilizer process industries, coal mines, iron and steel works, gold, copper and nickel refineries and concentration plants.

Due to the highly liquid nature of waste product which is supplied to the dams, a period of consolidation under its own weight is allowed to occur where the product effectively de-waters. The supernatant or overflow is then allowed to pass via a series of vertical penstocks in the dams which is then fed below the base of the dams to residual storage lagoons where further storage and evaporation takes place.

Because the heap leach process uses mechanical placement of ore whilst the slimes and tailings facilities use hydraulic techniques for finer fractions, then the liner selection is of generally thicker grades of HDPE for Heap leach whilst the slimes dams generally employ thinner to medium grades of liner.

In both cases, the liner design, selection and installation should ensure long term durability and chemical resistance with weld integrity over the operational life of the structure.

Solution ponds/channels

The liner systems used in these facilities are often more critical in terms of their aspects of design selection and installation than the adjacent waste or heap depositories which they serve. This is mainly due to the fact that there is a much greater hydraulic head of highly chemically–charged solutions exerted upon the liner system than there is in waste dams or heap leach which are equipped with basal drainage layers for unimpeded evacuation of liquids.

To cope with this additional need for security against potential leakage, the liner system is often designed with thicker membranes and can comprise multiple layers with intermediate drainage layers for the purpose of detecting and collecting any leakage which results from defects in the primary (upper) liner component, sometimes equipped with additional inspection tubes an pumps for the further recovery of product.

For further information please contact us.

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