Preliminary Economic Assessment – Samapleu Project

This technical report presents the proposed mineral processing plant design and carbonyl refining plant for the Samapleu Project based on testwork and engineering criteria.

Report context

This Preliminary Economic Assessment technical report, dated June 2020, describes the recovery methods for the Samapleu Project. The report presents the proposed mineral processing plant design comprising crushing, grinding, flotation, dewatering, and product load out facilities, along with a carbonyl refining plant for the production of nickel and iron powders. All throughput rates and metallurgical parameters are based on past and current testwork and may change according to ore composition.

Processing route

Mineral Processing Plant

The mineral processing plant consists of a crushing area and a concentrator where comminution, beneficiation, desulphurisation, dewatering, and product load out take place. The process is designed to produce 118 dry metric tonnes per day of nickel concentrate at 10.34% Ni grade, from ore containing 0.24% Ni. Copper concentrate will also be produced as a saleable product.

The process flowsheet includes crushing, grinding, rougher flotation, and cleaner flotation. The back end of the concentrator includes tailings and concentrate thickening, concentrate filtration, and material handling. Potential Acid Generating tailings from the concentrator will be filtered by a filter press and stacked outside the concentrator area. Non-Acid Generating tailings will be thickened and pumped to the tailings pond. Reclaiming water from the tailings pond has been considered in the process design to minimise fresh water make-up to the concentrator.

The nickel and copper concentrates will be recovered by a conventional flotation process. The beneficiation process has a global nickel recovery of 73.04%, with 71.08% recovered in the nickel concentrate at a grade of 10.34% Ni. The overall copper recovery is 92.31%, with 80.00% recovered in the copper concentrate at a grade of 23.00% Cu.

Crushing and Storage

Run-of-Mine mineralised material will be deposited into a grizzly feeder using a front end loader, at a maximum size of 600 mm, assisted by a rock breaker. The -90 mm undersized material from the grizzly feeder will discharge onto a conveyor and transported to a crushed ore pile. The +90 mm oversized material will feed a jaw crusher and then discharge onto the conveyor to the crushed ore pile. 80% of the ore in the stockpile will be -112 mm.

Primary Grinding Circuit

The primary grinding circuit includes a SAG mill that will be operated in a closed circuit with a double deck vibrating screen. The -3 mm screen undersize material is directed to the cyclone feed. The +3 mm oversized material reports back to the SAG mill feed. The SAG mill will have a diameter of 7.3 m and a length of 3.8 m, with a power draw of 3,100 kW.

Secondary Grinding Circuit

The secondary grinding circuit includes a ball mill and fifteen 510 mm diameter cyclones. The circuit is fed in a feed forward configuration from the SAG mill vibrating screen undersized discharge and ball mill discharge. The oversized material in the cyclone underflow flows into a ball mill. The ball mill operates in a closed circuit with the cyclones to obtain a grind size of 0.065 mm at the cyclone overflow, which feeds the flotation circuit. The ball mill will have a diameter of 6.1 m and a length of 9.4 m, with a power draw of 6,100 kW.

Bulk Flotation

The overflow from the cyclones, at 0.18% Cu grade and 0.24% Ni grade, passes through a conditioning tank before being pumped to the Cu/Ni rougher flotation circuit. Reagents used in the bulk flotation circuit include lime as a pH modifier, diethyl triamine, sodium metabisulfite, and carboxymethylcellulose as depressants, sodium isobutyl xanthate as a collector, and methyl isobutyl carbinol as a frother.

The Cu/Ni rougher flotation circuit recovers most of the copper and nickel from the ore, with 91% Cu recovery and 57% Ni recovery. The rougher flotation bank consists of six conventional flotation cells, 50 m³ each, providing 12.5 minutes of residence time. The pH target for the bank of cells is 8.2. Cu/Ni rougher concentrate is upgraded to 5.1% Cu grade and 4.3% Ni grade.

The Cu/Ni cleaner circuit further upgrades the concentrate recovered from the Cu/Ni roughers. The cleaner flotation bank consists of four conventional flotation cells, 1.4 m³ each, providing 5 minutes of residence time. The Cu/Ni cleaner upgrades the concentrate to 11.0% Cu grade and 9.0% Ni grade.

Copper Cleaning

The Cu/Ni separation circuit separates the copper and nickel, recovering copper in the concentrate and depressing nickel into the tailings. The separation flotation bank consists of four conventional flotation cells, 1.4 m³ each, providing 6.25 minutes of residence time. The pH target for the separation bank of cells is 12. The Cu/Ni cleaner recovers 80% Cu, and the concentrate is upgraded to 22.2% Cu grade.

The Cu cleaner column is the final upgrading stage of the copper cleaning circuit. The copper cleaning column is 1.5 m in diameter and 6 m tall, providing a residence time of 9.4 minutes. The concentrate is upgraded to a final grade of 23% Cu.

Nickel Cleaning

The Ni scavenger circuit recovers the remaining recoverable copper and nickel from the ore, with 6.4% Cu recovery and 14.2% Ni recovery. The scavenger bank consists of six conventional flotation cells, 50 m³ each, providing 15 minutes of residence time.

The regrind mill is fed with the Ni scavengers concentrate, the Cu/Ni cleaner scavenger tailings, the 2nd Ni cleaner tailings, and the underflow of the regrind cyclones. The 1st Ni cleaner circuit further upgrades the concentrate to 2.0% Ni grade. The cleaning bank consists of four conventional flotation cells, 5 m³ each, providing 5 minutes of residence time. The pH target for nickel cleaning banks of cells is 9.

The 2nd Ni cleaner circuit further upgrades the concentrate to 4.0% Ni grade. The bank consists of four cells, 0.3 m³ each, providing 3.75 minutes of retention time. The Ni cleaner column is the final upgrading stage of the nickel cleaning circuit. The nickel cleaning column is 1.5 m in diameter and 6 m tall, providing a residence time of 6.25 minutes. The concentrate is upgraded to a final grade of 6.3% Ni.

Tailings Desulphurisation

Tailings desulphurisation is accomplished in the pyrrhotite rougher circuit. The purpose of the desulphurisation circuit is to minimise the quantity of sulphide-rich gangue deposited in the tailings pond and therefore reduce the risk of acid-mine drainage. The pH target for the bank of cells is 5. Reagents used include sulphuric acid as a pH modifier, SIBX as a collector, and MIBC as a frother.

Concentrate and Tailings Dewatering and Handling

The Cu and Ni concentrates are treated in separate dewatering circuits. The concentrate is first thickened in a concentrate thickener. The thickened underflow at 55% solids is pumped to a holding tank, then to a filter press that produces copper filter cake at 92% solids and nickel filter cake at 90% solids. The nickel filter cake is fed via belt conveyors to CVMR. The copper filter cake is discharged into specialised concentrate containers.

Potential Acid Generating tailings are first thickened in a tailings thickener. The thickened underflow at 55% solids is pumped to a holding tank, then to a filter press that produces tailings filter cake at 88% solids. Non-Acid Generating tailings are thickened in a tailings thickener. The thickened underflow at 65% solids is pumped to the tailings pond.

Carbonyl Refining Plant

The carbonyl refining plant will recover nickel and iron from SFC. The feed material assay is 10.34% nickel, 26.58% iron, 1.36% copper, and 24.6% sulphur.

SFC will be roasted to convert the sulfide minerals to oxides in a Fluid Bed Roaster at 1050°C. The roasting operation has a processing capacity of 40,000 TPY. Sulphur dioxide production is 19,484 TPY. Calcined material production is 29,958 TPY with sulphur content less than 0.2%.

Calcined SFC will then be reduced in a rotary kiln with hydrogen at 650°C to convert the nickel and iron oxides to metallic nickel and iron respectively. The reduction operation processes 29,958 TPY with 70% hydrogen and 30% nitrogen in the reduction gas.

Nickel and iron will be extracted from reduced SFC in the form of volatile metal carbonyls through CVMR's carbonyl process at 130°C and 40 Bar pressure. The carbonylation operation produces 4,032 TPY of carbonyl nickel powder and 8,398 TPY of carbonyl iron powder. Residue production is 10,814 TPY.

The liquid mixture of nickel and iron carbonyls will be separated into iron carbonyl and nickel carbonyl through distillation. The designed purity of iron product is 99.9%. Nickel carbonyl gas will be sent to electrically heated, cylindrical powder decomposers to produce nickel powders. Liquid iron carbonyl will be sent to a vaporiser, and produced iron carbonyl gas will be decomposed in the iron powder decomposer.

Key reported parameters

Technical qualifications

All nominal throughput rates are based on the nominal production of 118 dry metric tonnes per day of nickel concentrate at 10.34% Ni grade. These figures are based on past and current testwork and may change according to ore composition. The sizing and dosages of flocculant systems will need to be confirmed with further testwork.

Source: Sama Resources Inc. NI 43-101 Technical Report, Preliminary Economic Assessment – Samapleu Project, June 2020, DRA/Met-Chem Ref.: G2622-Final-Report, Section 17 Recovery Methods.