Eritrea – This is following a comprehensive optimisation programme. The recovery ponds form a key sub-set of the processing plant configuration and allow higher potassium yields by capturing and evaporating waste brines exiting the processing plant.
The reduction in pond area has been achieved despite an increase in the processing plant throughput relative to the definitive feasibility study (DFS) and is the result of design enhancements in the brine circuit configuration.
The pond designs are also underpinned by over four years of comprehensive local weather data collection and evaporation tests.
Processing plant throughput was increased from 425 000tpa to 472 000 tpa following a debottlenecking exercise that was completed in May 2017.
“We are very pleased with the positive outcomes of the optimisation work on the recovery ponds and expect that there will be flow on benefits to the construction earthworks. The Colluli DFS demonstrated evaporation pond sizes significantly smaller than SOP brine projects as a direct consequence of the potassium salts being extracted from the resource in solid form. This benefit is unique to the Colluli resource,” says Danakali MD, Paul Donaldson,
The physical state of the raw feed is a key determinant of pond size
One of the distinguishing features of the Colluli resource is that the potassium salts used for sulphate of potash (SOP) production are present in solid form, allowing immediate processing following extraction from the resource using open cut mining techniques. This eliminates the need for pre-production evaporation ponds, allowing for significant savings in cost and time.
Primary resources for SOP production are typically potassium and sulphur rich brines, the processing of which commences with the generation of a harvest salt. This harvest salt is typically generated as the product of a multi-stage evaporation and precipitation process which progressively concentrates potassium and sulphur by selectively removing calcium, sodium and magnesium salts in early stage pre-production evaporation ponds.
Harvest salt production rates from brines are influenced by local weather conditions and potassium yields decrease with progressively increasing pond sizes (for unlined ponds) and the number of steps required to generate harvest salts.
The final potassium rich harvest salt generated as above is reclaimed and fed into a processing plant for conversion to SOP. Depending on the chemistry of the feed material fed into the processing plant, brines exiting the plant may be captured and directed to a set of recovery ponds to improve the overall potassium yield. These are small relative to pre-production evaporation ponds used in brine extraction.
Smaller pond size for Colluli is a key contributor to industry leading capital intensity
The Colluli DFS demonstrates industry leading capital intensity as a result of both the salts presenting in solid form and the exceptionally high ore grade. Low surface area recovery ponds is a key contributor to lower capital intensity.
Cut, fill and surface preparation volumes under evaluation
The cut, fill and surface preparation evaluation for the recovery ponds and overall site is currently underway. Results are expected shortly for direct comparison with the DFS.