Danakhil Potash Deposit — 2011 Technical Report

This report describes three conceptual processing options for potassium chloride recovery from the Danakhil potash deposit, each based on different mining and beneficiation approaches.

Report context

This 2011 technical report presents proposed recovery methods for the Danakhil potash deposit located in the Afar State of Ethiopia. The report details three processing options: flotation of open-pit mined sylvinite (Option 1); solar and thermal evaporation of solution-mined brine (Option 2); and solar evaporation followed by flotation of crystallized material from solution mining (Option 3). Each option is designed for a production capacity of 1 million tonnes of KCl per year, with the plant operating continuously for 7,500 hours per year.

Processing route

Option 1: Flotation of Material from the Open Pit

This option assumes open-pit mining, producing a KCl-containing solid feed. Processing stages include raw ore treatment, desliming, rougher flotation, cleaner flotation and leaching, scavenger flotation, reclaim brine and brine disposal, effluent flotation, and KCl product debrining, drying and screening. The dry KCl product is planned to have a purity of at least 95%.

Raw ore is stored in a bunker, then screened to separate material for crushing from material for direct repulping. Crushing liberates KCl crystals intergrown mainly with NaCl. The crushed salt is mashed with reclaim brine and water to dissolve carnallite and avoid precipitation of fine decomposition KCl. Wet screening divides solids into fine, middle and coarse fractions. The coarse fraction goes to wet milling and is returned to wet screening; the middle fraction proceeds to rougher flotation; the fine fraction goes to desliming.

Desliming removes fine insoluble material using cyclones. The cyclone overflow, containing most insolubles, is sent to thickening; the underflow proceeds to rougher flotation. Thickener overflow is reused as reclaim brine.

Rougher flotation processes feed containing approximately 20% to 40% KCl in solids (crude salt approximately 25% KCl) and produces a concentrate with over 80% KCl. Concentrate is fed to the cleaner flotation feed cyclone; the underflow goes to cleaner flotation and the overflow to effluent flotation. Rougher tailings are screened; the through fraction goes to tails thickening, while the oversize is crushed and sent to scavenger flotation.

Cleaner flotation enriches KCl to over 90% in solids. Tailings with over 20% KCl are recycled to rougher flotation. Concentrate is leached with water to dissolve NaCl, achieving the designated product purity.

Scavenger flotation recovers KCl from reground rougher tailings, separating KCl from insoluble material. Concentrate is sent to cleaner flotation; tailings are returned to screening.

Effluent flotation treats fine solids from cyclone overflows using column flotation. Approximately one third of the feed solids are KCl. Concentrate goes to leaching; tailings go to tails thickener.

Reclaim brine, a NaCl and KCl saturated solution, is recovered from thickener overflows. A disposal brine stream of 26 m³/h is discharged to control MgCl₂ content below approximately 50 g/l.

KCl product is debrined in centrifuges to 5% residual water, dried, and screened into fine, standard and oversize fractions. The oversize is crushed and returned to the product screen.

Option 2: Solar and Thermal Evaporation of Material from Solution Mining

This option uses solution mining to produce saline brine. Processing includes solar evaporation, thermal evaporation and NaCl crystallization, KCl crystallization, KCl product debrining, drying and screening, and solvent conditioning. The dry KCl product is planned to have a purity of at least 95%.

Brine from solution mining is led to solar evaporation ponds where water is removed and NaCl crystallizes. Brine is separated from NaCl crystals before KCl saturation (approximately 97%) and conveyed to the processing plant. Approximately 0.35 km² of evaporation surface is required for sylvinite mining brine; solar evaporation tests on site are recommended.

Thermal evaporation is performed in a four-stage evaporator system. The first stage is heated with steam; subsequent stages use vapour from preceding stages. NaCl crystallizes during evaporation and is dewatered by centrifuges. KCl brine at approximately 135°C undergoes flash evaporation where additional NaCl crystallizes and is removed.

KCl crystallization occurs via cooling in two sections: a brine-cooled section (four stages) and a water-cooled section (three stages). Crystallized KCl from stages 4 and 7 is dewatered by centrifuges. Mother liquor is largely recycled; approximately 5% is removed to limit MgCl₂ concentration.

KCl product is debrined in centrifuges to 5% residual water, dried, and screened. Solvent for solution mining is conditioned using vapour condensates from thermal evaporation and KCl crystallization stages, supplemented by heated cooling water to approximately 70°C.

Option 3: Solar Evaporation and Flotation of Material from Solution Mining

This option uses solution mining with solar evaporation followed by flotation of the crystallized material. Processing includes solar evaporation, crystallizate treatment, desliming, rougher flotation, cleaner flotation and leaching, scavenger flotation, reclaim brine and brine disposal, effluent flotation, and KCl product debrining, drying and screening. The dry KCl product is planned to have a purity of at least 95%.

Brine from solution mining undergoes two-stage solar evaporation. First, NaCl crystallizes in ponds requiring approximately 0.75 km² of evaporation surface. After brine separation from halite sediment, a second pond stage (approximately 2.25 km²) produces a Sylvite/Halite mixture. The mixture is harvested using surface miners and transported to the plant.

Crystallizate treatment follows the same screening, crushing, repulping and wet screening sequence as Option 1. Fine material goes to desliming, middle fraction to rougher flotation.

Desliming removes fine insoluble material (assumed from dust blown into ponds) using cyclones, with the same process flows as Option 1.

Rougher flotation processes feed containing approximately 20% to 40% KCl in solids (crystallizate approximately 31% KCl) and produces a concentrate with over 80% KCl. Flows are equivalent to Option 1.

Cleaner flotation, scavenger flotation, effluent flotation, and reclaim brine and brine disposal follow the same designs as Option 1, except that surplus reclaim brine is discharged directly as disposal brine without a specified rate.

KCl product debrining, drying and screening follow the same design as Option 1.

Key reported parameters

Technical qualifications

All processing descriptions represent preliminary flowsheet designs developed for a preliminary economic assessment. No actual operating data from the Danakhil deposit are reported. Options 2 and 3 specify that solar evaporation tests on site are recommended to define exact evaporation rates for pond sizing. The report notes that block schemes and mass balances are provided in referenced figures (Figures 19, 20 and 21) which are not included in this text. All product purity and performance values are design targets.

Source: Danakhil Potash Deposit , 2011 Technical Report, Section 17 Recovery Methods, pages 75–88.