Improvements in Hydrometallurgical Uranium Circuit Capital and Operating Costs by Water Management and Integration of Utility and Process Energy Targets LW de Klerk, MP de Klerk, D van der Westhuizen

Alkaline Leach Process Design Criteria Pinch Technology Water Removal Processes Evaporation Membrane Processes Improved Process Capital Cost Savings Value of Process Streams Operating Cost Savings

Conventional Alkali Leach Flow Sheet

Heat Requirement of Process Streams

Design Criteria Unit Value Feed rate tph dry concentrate 100 Concentrate Feed % moisture 35 Concentrate Composition ppm U, V 600, 1433 Leach Density % solids Na2CO3 in leach feed gpl 50 NaHCO3 in leach feed 20 Wash water for leach tails Wash displacements 1 NaOH in SDU precipitation Residual gpl 6 Tailings

Pinch Technology Systematic methodology for reducing energy consumption of processes by calculating feasible energy targets Achieving targets by optimising heat recovery systems and energy supply Graphically shown by plotting enthalpy flows (kW) against temperature for streams being heated and cooled

Pinch Technology – Heat Profile of Process Streams

Pinch Technology – Heat Profile of Process Streams without Solar Pond

Pinch Technology – Heat Profile of Power Plant

Heat Profile of Power Plant as Hot Utilities

Heat Profile of integrated Process Streams and Hot Utilities

Heat Requirement of Process Streams integrated with Power Plant

Effect of Concentration on Plant Sizing Residence time is related to the volumetric flow and sets the sizing of process plant. Solid content of slurry streams and the tenors of solutions limit the concentrations that can be used. Increasing solid content from 35% to 45% reduces flow by 28%, and the cost of equipment by 20%. Leachate dissolved solids content is 20.4%. With minimum water removal this increases to 26.5% before SDU precipitation. Increasing this to 40% decreases the flow rates by 18% and the equipment costs by 13% A combination of these two changes can reduce capital cost by $4.2m

Water Removal Processes Evaporation Solar pond Cooling Towers Evaporators Membrane processes Nano Filtration Reverse osmosis

Evaporation Solar ponds Cooling Towers Evaporators dependant on seasonal weather, can take up a large area, costly if lined, introduce contamination, result in seasonal operating conditions make environmental approvals more difficult Cooling Towers increase the loss of water from the hot stream by efficiently using the heat in the feed stream for evaporation in areas with low wet bulb temperatures and a warm stream sent to the pond, a cooling tower can reduce the a solar pond evaporation area by 40%-50%. Evaporators use approximately 1 ton of steam to evaporate each ton of water in a single effect evaporator and for each subsequent stage approximately 0.9 tons of water can be evaporated using the steam generated from the previous stage. capital intensive but can be economic if heat is available at low cost, which may be the case where on site power is generated.

Membrane Processes Nano Filtration cross flow, pressure driven membrane process membrane pore size corresponding to molecular weight cut-off of approximately 200 –1000 dalton operating pressures of 150–500 psi (10 –34 bar). a looser membrane operated at a relatively low pressure. Larger molecules are held back and smaller molecules allowed through. In the alkaline leach circuit this allows partial separation of U and V complexes, sulphates and carbonates from water and non complexed ions such as sodium and chloride.

Membrane Processes Reverse osmosis a membrane process where a tighter membrane is operated at a relatively high pressure Most ions are held back and mainly water allowed through producing a relatively pure water stream and concentrated brine. In the alkaline uranium each circuit this allows recovery of water from the circulating streams producing water for residue washing and disposal of a more concentrated brine.

Membrane Processes remove water and partially separate components level of circulating impurities can be reduced and a much higher concentration of valuable components is possible stream size of SDU precipitation can be reduced by up to 74% saving capital of $5.7m

Improved Process based on a U3O8 Corp project, Laguna Salada sized to the same design criteria as the conventional flow sheet is used as a case study developed without evaporation ponds for environmental reasons the uranium mineral contains significant amounts of reactive gypsum project has access to a power supply network and a gas pipeline so no savings by integration of the power plant and the process were available.

Improved Process Requirements concentrate U and V to a low volume SDU plant feed stream reduce NaHCO3 tenor in the SDU feed stream and thus reduce NaOH consumption recover rather than evaporate excess water recover sodium carbonate and sodium bicarbonate to be re-used in the leach circuit

Improved Process Solution two stage membrane plant first stage retaining uranium to a concentrated retentate which becomes the feed to the SDU precipitation circuit, thereby minimising the size of and reagent demand in the SDU circuit. contain, together with uranium, the majority of the vanadium and sodium sulphate in the PLS, as well as high levels of leach reagents sodium carbonate and sodium bicarbonate

Improved Process Solution second stage recovers the remaining leach reagents and the majority of the vanadium second stage permeate resembles high quality water containing some vanadium, some sodium carbonate and bicarbonate is returned to the leach permeate from the PLS membrane concentration circuit is used as wash liquor on the gypsum leach vacuum filters. permeate, supplemented with fresh water, is used as wash liquor on the post leach (fine tails) vacuum belt filters.

Capital cost savings Direct cost of conventional plant ~ $60M 82% reduction in the size of the SDU plant (volume down from 143 to 26 m3/h) reduces the cost of the SDU plant by 68%, and total direct cost by 7% replacing evaporation plant with the two stage membrane plant adds $3.4 million to the capex compared to the case with a cooling tower and a smaller evaporation pond this adds an additional $1.0 million increase is justified by reducing operating costs ( lower product loss and reagent consumption)

Optimised Flow Sheet

Operating Cost Savings conventional flow sheet expected to operate at an annual cost of $33 million, two thirds of which is associated with exorbitant consumption of sodium carbonate and sodium hydroxide due to the high reactive gypsum content. incorporation of the gypsum removal and innovate PLS treatment plants reduces the cost of reagent by a staggering $19 million per year. annual operating cost associated with the gypsum removal and innovative PLS treatment plant amounts to $6.8 million, decreasing the overall operating cost for the improved plant to $20.8 million per year. If power was produced on site, the waste energy could be utilised and result in savings of $1.7m or 8% of operating costs.

Summary considering energy integration and water management can make large improvements to project viability membrane technology can radically change process flow sheet optimal solution dependant on site conditions, the particular ore behaviour and specific to each project and need to investigate on a case by case basis techniques applicable to wide range of hydromet processes

Authors: LW de Klerk, MAusIMM, Consultant, Project and Process Development, 16 Kariong Circuit, Duncraig, WA. Email louiswdeklerk@yahoo.com.au MP de Klerk, Process Engineer, Project and Process Development, 16 Kariong Circuit, Duncraig, Email matthewpdeklerk@outlook.com D van der Westhuizen,, Consultant, Process Simulation and Development, 7 Armson Avenue, Magill, Adelaide, Email dwesthuizen0@gmail.com A paper on which the presentation has been based is available from the authors