Processing
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1. ZCDC Processing Overview
Our diamond recovery processes entail the liberation of the diamonds from the host rock followed by concentration and final picking of the diamonds from the concentrate. This is achieved through the use of world class systems which incorporates modern ore processing and recovery technologies. The processes are designed to maximize recovery of diamonds from the ore while preserving the value of the recovered diamonds. This is in line with our Diamond Value Management standards.
We are therefore in constant search for new and ground-breaking technologies to continuously improve our processes Our research and development department optimizes recovery processes and equipment ensuring that the achieved recovery efficiencies conform to the industry standards and best practices.
ZCDC is engaged in various process improvement projects that are aimed at reducing operating costs while maintaining high recovery efficiencies.
2. Processing Stages
The ore processing and recovery processes at ZCDC entails the following major stages:
- Liberation (Crushing & Screening)
- Concentration (DMS, XRT)
- Final Recovery and Sorting
Liberation
Liberation of diamonds from the host conglomerate rock is achieved through crushing and screening to achieve the ore particle sizes needed in the concentration stages of the process. This is done in conformance with the Diamond Value Management (DVM) standards which at this stage is aimed at preserving the diamond value and maintaining revenue potential by minimizing diamond damage during the crushing stages. Size reduction of ore is thus achieved in a stage-wise manner using primary, secondary and tertiary crushers.
Concentration
Concentration of the liberated ores is achieved through the Dense Media Separation (DMS) and XRT technology.
Feed preparation
Prior to the DMS process the liberated ore is subjected to a Feed preparation stage. During the feed preparation stage, fine material is removed from the ore using high pressure water in the wet screening plants.
Fine material affects downstream processes thereby reducing recovery efficiency. The screening process also ensures that the feed to the downstream plants is within the required top and bottom cut off size ranges.
Dense Medium Separation (DMS)
The Dense Media Separation uses gravity separation and density differentials technique is used for primary concentration in the diamond recovery process. At this stage, ore and a ferrosilicon pulp mixture of required density is fed to a DMS cyclone where separation occurs. The centrifugal and drag forces developed in the cyclone create a swirling motion resulting in lighter particles reporting to overflow (floats) and heavier particles to underflow (sinks). Due to their high specific gravity, diamonds are recovered in the cyclone underflow as diamond rich concentrate.
X-Ray Transmission (XRT)
XRT sorting is used for final diamond recovery. This technology is based on the extent of X-ray absorption by different minerals. Since diamonds consist of carbon, which has a low atomic number, it absorbs less radiation than other minerals which contain heavy elements. Therefore, the X-ray images generated by XRT sorters for the different minerals enable diamonds to be detected against a reference calibration density. The detected diamonds are then recovered using a compressed air ejection system.
Final Recovery & Glove box Operation.
Rough diamonds are hand-picked from XRT concentrate in secure glove box units. The picked rough diamond categories are Gem, Near-gem and Boart. Caustic fusion and acid digestion processes operated at high temperatures are used to liberate any diamonds that may still be attached to the host gangue material.