This technical report describes the processing route for the Ramu nickel-cobalt operation, covering the wash plant and beneficiation plant at KBK and the hydrometallurgical refinery at Basamuk, with supporting production data from 2012 to 2018.
Report context
This October 2019 technical report addresses the Ramu NiCo project, which incorporates two processing plants at the KBK site (the wash plant located adjacent to the open pits and the beneficiation plant located about 1.5 km from the wash plant) and a third processing plant, the Basamuk refinery, located about 135 km from KBK on the coast about 75 km southeast of Madang. The report states that detailed design of the three processing plants is considered commercially sensitive and the description is restricted to generalities. The report notes that the author has inspected the plants, had access to recent production reports, and has been provided with information on planned plant upgrades for progressive production increase. The report considers that the two KBK processing plants have the capability to produce the required tonnages of ore feed to the Basamuk hydrometallurgical plant and the Basamuk plant can treat the ore to produce the budgeted amount of mixed nickel-cobalt hydroxide product (MHP) annually.
Processing route
Washing Plant
The first stage in treating the mined ore requires washing the feed material to remove coarse, barren rocks. The wash plant comprises four identical trains in parallel. The first stage in each train is the ore bin that receives the "as mined" material from trucks. Ore is moved from the bin using an apron feeder into a rotary drum washer which has internal weirs to retard the flow and water sprays to wash the ore. At the discharge end of each drum there is a screen that removes material smaller than 50 mm; the coarse +50 mm material discharges onto a common conveyor and out onto a stockpile, from where it is transferred by front-end-loaders and trucks to be used as road metal and backfill. The -50 mm material drops into two parallel logwashers for further scrubbing. The logwasher is an inclined trough fitted with a rotating screw that moves the coarse material up to a discharge point; water is sprayed into the logwasher to create a slurry that overflows the lower end of the unit into pumps that send the -3 mm to the beneficiation plant. The coarse material discharges to a common conveyor and thence to a bank of three vibrating screens which separate the -3 mm to the undersize which then joins the other -3 mm material to be pumped to the beneficiation plant. The +3 mm material is conveyed to a stockpile to be also removed as waste by the front-end-loader and truck fleet. The hydraulically mined material is pumped from the mine to the bank of vibrating screens to also separate the -3 mm material for beneficiation.
Process water is provided from the nearby river and is also recycled from the beneficiation plant. Electrical power for the wash plant is reticulated from the six-unit diesel power generation plant located adjacent to the beneficiation plant.
The wash plant with the four trains is designed to process about 7.5 Mtpa of wet ore or about 4.1 Mtpa of dry ore. About 15% of the material is rejected to waste. The 2018 production details report 6.35 Mt of wet ore treated resulting in 3.72 Mt (dry) of feed to the Basamuk plant or about 58.5% of the wet feed material. The report states that Ramu has budgeted that 7.5 Mtpa wet ore will be fed in future years with 4.11 Mtpa (55%) being the dry ore feed to the wash plant.
Beneficiation Plant
The purpose of the beneficiation plant is to remove chromite from the ore feed to be pumped to the Basamuk plant and to produce a chromite concentrate for sale. The beneficiation plant receives the -3 mm slurry from the wash plant in two large 10 m diameter tanks. The plant comprises two identical trains, each with a 10 m diameter feed storage tank from which the slurry is pumped through a bank of hydrocyclones. The hydrocyclone overflow, or "slimes" at a size distribution of -53 µm is pumped over a trash screen and then to the product thickener. The coarser +53 µm to -3 mm hydrocyclone underflow is fed to a bank of 13 triple-start spiral concentrators. The tailings, or overflow from the spirals containing the lighter material is fed to the desliming hydrocyclones; the heavier product is forwarded to a bank of 26 shaking tables that further concentrates the heavier chromite particles as feed to a spiral classifier to remove fugitive "slimes", with the spiral underflow, or coarse material, sent to one of two common magnetic separators. The magnetic separators remove the free chromite particles from the lower quality material which will be discharged as a tailing product backfill into the pits. The chromite product is stockpiled and then trucked to a loading area about 5 km downhill from the processing plant. The chromite product is reclaimed by a front-end-loader into highway haulage trucks which transport the material to Lae for shipment to market.
The lighter material from the spirals and from the shaking tables is pumped to a bank of hydrocyclones set to separate the slurry to be pumped to the Basamuk refinery. The hydrocyclone underflow which is the coarse material is ground in a standard ball mill to reduce all material to suitable size.
The ground and separated material is screened to remove any "trash" and then thickened in large settling thickener. The thickener underflow at 15% to 19% solids w/w is stored in one of four 30 m diameter storage tanks, and is then pumped over 135 km to the Basamuk plant at about 1,600 cubic metres per hour.
Basamuk Refinery
Slurry Receipt
The slurry pumped from the KBK plant to Basamuk refinery at grades of approximately 1.08% Ni and 0.12% Co. The slurry can be discharged into receiving storage tanks, from which the slurry is pumped to a thickener to allow solids density to increase to greater than 30% solids w/w.
High Pressure Acid Leach (HPAL)
The thickened underflow slurry is pumped to a slurry storage tank for each of the three HPAL circuits. Each HPAL circuit comprises a high-pressure autoclave which has three stages of pre-heat vessels and respective pumping and three stages of heat recovery (flash) vessels, all interconnected. Slurry is pumped from the storage vessel into the first pre-heat vessel along with heat that has "flashed" from the third or low temperature flash vessel. The heated slurry is then pumped using a conventional centrifugal slurry pump to the second stage of pre-heat where the second stage flash gases are directed to heat the slurry even further. The slurry from second stage pre-heat is pumped to the third pre-heat stage using three centrifugal pumps in series along with gases from the first or high temperature flash stage. The slurry from the third stage preheat vessel at around 200°C is then pumped into the autoclave using a high-pressure positive displacement pump. Each autoclave is equipped with two pumps, each with its own discharge into the autoclave and capable of pumping full throughput but generally operating in parallel at about 50% capacity, to provide circuit redundancy.
The autoclaves are designed to operate at a temperature of about 250°C and pressures of about 43 bar or 4,300 kPa. High-pressure steam is injected into the autoclave to raise the pressures to 4,300 kPa. Each autoclave is lined with a high quality titanium and has multiple compartments, each equipped with agitators. Slurry residence time is about 60 minutes per autoclave. Sulphuric acid is injected into the autoclave at a rate required to achieve target extraction of greater than 95% for nickel and cobalt.
Partial Neutralisation (PN)
The slurry discharge from the third flash vessel has a high level of free acid which must be partially neutralised to allow the further downstream processing to recover the nickel and cobalt values. Neutralisation is undertaken using locally sourced limestone and the free acid is effectively reduced to a low level. Compressed air is added to assist oxidisation of ferrous iron to ferric iron which will precipitate into the slurry. The air also removes minor CO2 build-up in the slurry flow. The PN circuit is made up of multiple agitated vessels into which the limestone slurry is injected and tanks can be by-passed for maintenance if necessary. The neutralisation time should be greater than 90 minutes and is affected by other recycle streams from the second stage of Fe and Al removal as well as the second stage of Ni and Co precipitation. The reported neutralisation time ranges from 3 to 4 hours.
Counter-Current Decantation (CCD)
The neutralised slurry is fed to a seven-stage series of thickeners where the slurry continues in a forward direction from CCD1 down to CCD7; the CCD thicker overflows are pumped counter-current to the slurry flows. The final solids product from CCD7 is sent to residue neutralisation before discharge as a final tailings product. Process control has been set up to ensure that the underflow solids density is controlled at about 45% solids w/w prior to discharge to tailings neutralisation to ensure the maximum recovery of Ni and Co into the overflow liquor. The overflow from CCD1 contains all the recoverable Ni and Co in solution, which is then fed to the Fe and Al precipitation circuit.
To aid settling, a flocculant or settling agent is added to the CCD thickener feed flows; to assist metal recovery, a high wash ratio is provided. To allow the 36 m diameter thickeners to perform efficiently, the feed to the thickener feed well is equipped with an eduction system to increase the feed solids dilution. Flocculant is added to each CCD thickener to assist settling. The extra demand for aqueous is satisfied by recycling the second-stage Ni/Co precipitation circuit thickener overflow.
Iron and Aluminium Removal
Prior to recovering the two main metals, Ni and Co, it is necessary to reduce the amount of iron and aluminium in the liquor. Ramu undertakes this in multi stages of precipitation in order to reduce the amount of Ni and Co co-precipitation. The operating scenario relates to maximising the precipitation of the Fe and Al while keeping the Ni and Co precipitation to a minimum; higher pH allows better removal of Fe/Al but more Ni and Co will also precipitate. The first stage of Fe/Al precipitation entails addition of limestone to the liquor to raise the pH and allowing the reaction time to be about six hours using at least six tanks.
The objective in the first stage is to remove up to 80% of the Al and 60% of the Fe while minimizing Ni/Co precipitation. The resultant slurry is thickened in a single thickener unit with the thickener underflow sent to a plate-and-frame filter. The filter cake is repulped using barren liquor and the slurry is pumped to tailings neutralisation. In order to maximise the Fe precipitation compressed air is injected into the reaction vessels to further oxidise the Fe2+ to Fe3+. The thickener underflow density is controlled at about 35% to 40% solids w/w.
The thickener overflow and the filtrate from the filter is then fed to the second stage Fe/Al precipitation circuit. More limestone is added to allow the pH to rise which requires about four hours and four reaction vessels. The second stage Fe/Al precipitation slurry is then thickened to remove the precipitated solids. Air is added as in the first stage precipitation and seeding is also used if necessary to maintain the thickener underflow density. The solids from the second stage thickener are pumped to the PN circuit for re-leach of the co-precipitated Ni and Co. The overflow from the thickener is fed to the Ni/Co precipitation circuits.
Nickel and Cobalt Precipitation
The liquor from the Fe/Al precipitation circuits is treated in a further precipitation circuit using sodium hydroxide to precipitate a mixed hydroxide product (MHP). The Ni/Co precipitation takes place in two stages. The reactor discharge is fed to a thickener, with the thickener overflow fed to the second stage circuit while the underflow is split as seed and as product. The product stream feeds a filter, with the filtrate also sent to the second stage circuit. The filter cake is discharged into a storage bin from which the material is packaged into one tonne bags ready for shipment to the market.
The second stage of Ni/Co precipitation is effectively a means to ensure that overall metal recovery is maximised.
Tailings Treatment
Tailings treatment requires neutralisation before the slurry is discharged to the DSTP. The circuit comprises a bank of five reactors and slaked lime is added to the slurry to bring pH to over 8.0. Once neutralised the slurry is pumped to the DSTP station where it is then discharged.
Plant Reagent Supply
The principal reagents consumed in the Basamuk plant are:
1. Sulphuric acid is the main reagent consumed in the HPAL process. The consumption rate is about 900 ktpa of acid. Ramu has installed two acid plants that burn elemental sulphur to produce greater than 98.5% sulphuric acid. The plants are double catalysis and double adsorption units. The sulphur is purchased on the open market and can be delivered from a variety of sources such as North America or the Middle Eastern Gulf. The production of acid produces a significant amount of high-pressure steam as well as low pressure steam. The high-pressure steam is used for HPAL heating and the low pressure steam is used throughout the plant. Power co-generation has not been considered, as most of the steam is consumed in the process.
2. Limestone and lime are also reagents with high overall consumption rates. Limestone is mined at a quarry near the Basamuk plant and is transported to the plant with a large stockpile storage capacity to accommodate wet season quarrying delays. The limestone is reclaimed and crushed in a two-stage jaw and cone crushing circuit with the fines sent to a grinding mill circuit for further size reduction and slurrying ready for use in the plant.
3. Flocculants comprise a significant component of reagent requirements.
4. Other reagents and consumables are brought in as required and comprise grinding balls for the limestone mill, burned lime, platinum catalyst for the acid plants and sodium hydroxide for Ni/Co first stage precipitation.
Plant Ancillary Services
A number of ancillary plants are necessary for the operation of the Basamuk plant:
1. Auxiliary steam production is necessary to augment steam required for the HPAL units if acid plant steam is insufficient. Two 245 t steam boilers have been installed and operate burning mostly residual oils collected throughout the operation.
2. Compressed air supply is conventional utilising conventional air compressors producing high pressure air for use throughout the plant including the air injection in the neutralisation and precipitation steps for ferrous to ferric oxidation.
Production Capacity
Production from the KBK plant is dependent upon the ability of the Basamuk plant to take feed. In the initial couple of years, both plants were experiencing ramp-up and the Ramu experience was similar to a number of other lateritic nickel/cobalt operations, taking some time to achieve design throughput and product output. The KBK plant took approximately four years to ramp up to the planned throughput, though the ramp-up was interrupted in 2016 because of an incident at the Basamuk plant which forced a three-month shutdown. If the KBK plant had operated for the full year in 2016, it is estimated it would have produced in the order of 30,000 t of product, or 90% of budget. In years 2017 and 2018, output exceeded budget by 6% and 9% respectively. Chromite production has slowly increased but remains slightly below target, however this is related to ore grade and is not material to the plant performance.
One of the main parameters that affects the production rates and overall operability of the two plants is equipment availability and utilisation. The KBK wash plant has been designed with four trains, which ensures that a reasonable amount of material is always being sent to the beneficiation plant. Storage capacity of beneficiated material is substantial, with four large storage vessels, allowing a reasonably steady flow of feed slurry to the Basamuk plant. The beneficiation plant has little rotating equipment, with the principal equipment being pumps, the one grinding mill and a conveyor. These items have been reasonably well maintained with beneficiated product to Basamuk exceeding design parameters over the past two years.
The Basamuk plant is a complex hydrometallurgical processing plant consisting of interdependent unit operations. Ramu has installed interstage storage as this is critical in reducing impact from a temporary shutdown of a circuit either upstream or downstream. Also, most circuits have surplus capacity, such that one tank could be taken off-line without affecting circuit performance. Each autoclave has two feed pumps, allowing production to continue with one pump down. The installation of two acid plants allows continuous operation for reasonable periods with one acid plant down. The design operating time for the HPAL plant is 7,500 hours/year or 85.6% of the time. HPAL plants generally operate continuously until a circuit shutdown is required. Past practice has evolved from shutdowns every eight months to now experiencing a shutdown at about every twelve months. By good management, scheduling of shutdowns has improved as well as incorporating acid plant shutdowns which are scheduled for 12 month intervals.
Key reported parameters
| Parameter | Units | 2012 Actual | 2013 Actual | 2014 Actual | 2015 Actual | 2016 Actual | 2017 Actual | 2018 Actual | Design/ Budget |
|---|---|---|---|---|---|---|---|---|---|
| Wash plant feed (wet) | Mt | 0.973 | – | 5.949 | 6.105 | 3.876 | 5.523 | 6.350 | 7.477 |
| Beneficiation product (dry)* | Mt | – | 1.252 | 2.273 | 2.784 | 2.270 | 3.601 | 3.719 | 3.400 |
| Nickel in product | % | 1.01 | 1.02 | 1.05 | 1.12 | 1.13 | 1.09 | 1.11 | 1.08 |
| Cobalt in product | % | 0.09 | 0.10 | 0.10 | 0.11 | 0.11 | 0.11 | 0.10 | 0.12 |
| Chromite production | dry kt | 18.0 | 32.7 | 32.0 | 51.4 | 52.8 | 90.1 | 92.1 | 95.4 |
| MHP wet | t | 43,772 | 103,615 | 180,170 | 178,977 | 153,899 | 237,445 | 241,133 | 220,518 |
| MHP dry | t | 13,783 | 29,736 | 57,415 | 65,286 | 57,824 | 89,947 | 92,258 | 83,797 |
| Nickel in MHP | % | 38.3 | 40.4 | 36.6 | 39.2 | 38.5 | 38.5 | 38.3 | 39.0 |
| Contained Ni (dry) | t | 5,283 | 12,023 | 20,986 | 25,582 | 22,268 | 34,666 | 35,355 | 32,681 |
| Cobalt in MHP | % | 3.4 | 3.79 | 3.72 | 3.84 | 3.79 | 3.68 | 3.59 | 3.8 |
| Contained Co (dry) | t | 469 | 1,126 | 2,133 | 2,505 | 2,190 | 3,308 | 3,275 | 3,346 |
| Nickel recovery (Basamuk) | % | – | 93.8 | 87.7 | 82.3 | 87.1 | 88.0 | 87.0 | 89.0 |
| Cobalt recovery (Basamuk) | % | – | 92.3 | 90.2 | 83.3 | 86.2 | 86.6 | 86.0 | 82.0 |
Project website: https://www.nickel28.com/
*Beneficiation plant product is Basamuk plant feed. Design/budget parameters relate to design parameters for Table 17.1 and design parameters for Table 17.2.
Additional design parameters from the report:
| Parameter | Value | Basis |
|---|---|---|
| Wash plant design capacity (wet) | 7.5 Mtpa | Design |
| Wash plant design capacity (dry) | 4.1 Mtpa | Design |
| Design waste rejection | 15% | Design |
| Slurry solids content to Basamuk | 15% to 19% w/w | Design/operating |
| Slurry flow to Basamuk | 1,600 m³/h | Design |
| Slurry Ni grade to Basamuk | 1.08% | Design parameter |
| Slurry Co grade to Basamuk | 0.12% | Design parameter |
| Autoclave operating temperature | 250°C | Design |
| Autoclave operating pressure | 43 bar (4,300 kPa) | Design |
| Slurry residence time in autoclave | 60 minutes | Design |
| Target Ni/Co extraction in HPAL | >95% | Design target |
| PN neutralisation time design | >90 minutes | Design |
| PN neutralisation time reported | 3 to 4 hours | Operating data |
| CCD underflow density target | 45% solids w/w | Process control target |
| First stage Fe/Al precipitation reaction time | ~6 hours | Design/operating |
| First stage Al removal objective | Up to 80% | Design objective |
| First stage Fe removal objective | Up to 60% | Design objective |
| First stage Fe/Al thickener underflow density | 35% to 40% solids w/w | Operating target |
| Second stage Fe/Al precipitation reaction time | ~4 hours | Design/operating |
| Sulphuric acid consumption | ~900 ktpa | Operating data |
| HPAL plant design operating time | 7,500 hours/year (85.6%) | Design |
Technical qualifications
The report notes that detailed design of the three processing plants is considered commercially sensitive and the description is restricted to generalities. The report further states that it does not name report authors or qualified persons. The information presented is based on inspection of the plants, access to recent production reports, and information on planned plant upgrades. The production data tables include a note that the annual budget relates to design parameters. The report does not provide specific testwork results from mineral processing or metallurgical testing, which are referenced to Section 13 of the full technical report.
Source: Ramu Nickel Cobalt Operations , 2019 Technical Report, October 2019, Sections 17.1 to 17.5.
