Tanzania – Since the release of the Ngualla bankable feasibility study (BFS) of April 2017, Peak Resources has been able to improve the annual operating margin (EBITDA) of the project by 20% or US $29 million from $145 million a year at BFS to $174 million a year as a result of process optimisation work.
In addition to this, the company has been able to reduce unit operating costs by 5.7% from US $34.20/kg of neodymium-praseodymium oxide (NdPr) to $32.24/kg of NdPr.
Post Tax and Royalties NPV(10) and IRR increased from $ 445 million and 21% at BFS to $579 million and 24%.
Moreover, the company was also able to increase annual NdPr production has by 16% to 2 810 tpa.
“This is an outstanding outcome by the Peak Resources team that drives Ngualla’s already low unit costs even lower and delivers a large increase in operating margin, reinforcing Ngualla as the leading development project for NdPr,” says Peak Resources MD Darren Townsend.
“The more than 100% increase in NdPr prices this year, combined with these significant operating improvements support our main focus now, which is to progress a mining licence application in order to fast track Ngualla towards production in time for the increased demand for NdPr from electric vehicles,” he says.
Process optimisation work
Peak Resources has been able to increase capacity through Ngualla’s multi-stage processing facility. The final, lower cost flotation collector selected in the BFS for use in the on-site processing plant at Ngualla has a lower residence time compared to the equivalent pilot plant regime.
A new study has identified that the lower residence time allows the production capacity of the Ngualla facility to be increased over the BFS throughput with the addition of $4 million extra capital expenditure at the Ngualla site.
The optimisation work has also allowed for a 16% increase in NdPr production. The increased output available from the Ngualla facility can be treated at the Teesside Refinery with only a relatively small adjustment to the plant design, estimated at a $5 million increase in the total construction capital at the refinery.
Collector screening testwork
New studies on the testwork completed to select the optimal flotation collector for the BFS show that the final lower cost reagent regime chosen not only produced comparable flotation performance (grade and recovery) to the equivalent pilot plant regime but also has the added advantage of faster flotation kinetics.
The testwork was undertaken at bench scale by reagent suppliers and also the Peak Resources team at ALS Metallurgy, Perth, on a composite sample of Ngualla’s ore similar to the pilot plant feed, achieving grades consistently over 40% rare earth oxide.
The lower residence time offers a significant advantage for an increase in flotation circuit production capacity without changing the existing BFS plant design.
A capacity analysis of the multi stage processing facility at Ngualla identified the rare earth flotation stage as the primary bottleneck in the circuit as designed for the BFS. The capacity of this stage of the circuit is a function of the size and number of the flotation cells and the residence time that the ore must stay in each cell to achieve the desired recovery. A reduced residence time thus means the amount of ore passing through the circuit can be increased without changing the size or number of cells.
Removing the process bottleneck from the rare earth flotation cells shifts the capacity constraint to the ball mill. By maximising the throughput of the existing ball mill at an additional capital cost of $4 million and a slightly accelerated BFS mining schedule, the average mill feed and corresponding concentrate production can be increased by approximately 16% per annum.
Analysis of the Teesside refinery identified that the capacity constraints to increasing the throughput to take the additional processed product from Ngualla were the three solid liquid separation processes. Internal estimates to increase the required capacity of these filters and thickeners are an additional capital of $5 million.