1. 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

2. 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

3. Conventional Alkali Leach Flow Sheet

4. Heat Requirement of Process Streams

5. 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

6. 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

7. Pinch Technology – Heat Profile of Process Streams

8. Pinch Technology – Heat Profile of Process Streams without Solar Pond

9. Pinch Technology – Heat Profile of Power Plant

10. Heat Profile of Power Plant as Hot Utilities

11. Heat Profile of integrated Process Streams and Hot Utilities

12. Heat Requirement of Process Streams integrated with Power Plant

13. 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

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

15. 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.

16. 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.

17. 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.

18. 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

19. 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.

20. 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

21. 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

22. 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.

23. 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)

24. Optimised Flow Sheet

25. 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.

26. 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

27. Authors:
LW de Klerk, MAusIMM, Consultant, Project and Process Development,
16 Kariong Circuit, Duncraig, WA.
MP de Klerk, Process Engineer, Project and Process Development,
16 Kariong Circuit, Duncraig,
D van der Westhuizen,, Consultant, Process Simulation and Development,
7 Armson Avenue, Magill, Adelaide,
A paper on which the presentation has been based is available from the authors