PROJECT DEVELOPMENT FRAMEWORK
A project can be developed in a variety of ways depending on project specific requirements, but the below list presents a typical development timeframe and stages for taking a project from bench-scale testwork through to the commissioning of the commercial DNi Process™ plant.
DNi has tested over 90 different ore samples from almost 30 different projects from around the world in their process laboratory embedded within Australia’s CSIRO Minerals Division. Its pilot plant facilities – which comprise the full process flowsheet from ore leaching through to acid recovery – are located on-site with the process laboratory and have operated for a total of 19 campaigns conducted over most of 2013.
The general stages for developing a nickel laterite project are shown in the table below, and include expected durations and sample requirement for each phase. Depending on the project requirements, these stages can be flexibly tailored to suite the needed timeframe.
|Bench Scale Leach Amenability Testwork||1-2 kg representative sample||3 weeks||Basic leach extractions – general test for ore suitability.|
|Full Bench Scale Testwork Program||10-15 kg representative sample
|4-6 months||Detailed report with:
Optimised leach extractions;
By product compositions;
MHP compositions; and
Overall recovery based on bench testwork.
|Pre-feasibility study (optional)||Previously completed full bench scale program, required throughput and location, unit cost data||3 months||Conceptual flow diagram.
Preliminary equipment list.
Order-of-magnitude capital and operating cost estimates.
|DNi Pilot Plant Operation||Testwork agreement, ~30-60 tonnes representative sample||4-6 months||Detailed report with:
Reagent consumptions; and
|Process design development/ feasibility study||Licence agreement
Key design criteria
|6 months||Process design package containing:
Process design specifications;
Mass and heat balance;
Detailed equipment specifications; and
Capital and operating cost estimates to ± 15%.
|Engineering design, construction and commissioning||Approval of contractor||Approval of mass balance, process flow diagrams and valve and instrument diagrams.
Ongoing technical support.
Bench Scale Leach Amenability Testwork
An typical first step in the development of a DNi Process™ project is to treat a small amount of representative ore in a bench scale batch leach test. This test is relatively simple to perform and can give a good indication of the leach performance of the particular ore under DNi Process™ leach conditions. The tests are quick and inexpensive and do not need a large sample. Typically a single test will be conducted under acid overdose conditions to give an idea of the maximum achievable leach extractions for the particular ore mineralogy. Being such a small and quick test, it is a good way to assess the ores’ amenability to the DNi Process™, before committing to a full lab scale program.
The bench scale leach amenability testwork are typically conducted in a 1L vessel on 200-350g of sample, under the DNi Process™ leach conditions. A simple amenability test may take only one acid dose condition and provide maximum leach extractions, but a more inclusive set of tests could be conducted if required, for example on multiple ore bodies or various acid dosage rates. Kinetic samples can also be taken if required, however these are more costly and are always included in the Full Bench Scale Testwork Program. Ideally 1-2 kg of sample would be needed, sized 100% passing 0.5mm, however it will be possible to conduct a test on any sample greater than 200g.
Full Bench Scale Testwork Program
The next step in developing a DNi Process™ project is a Full Bench Scale Testwork Program on a representative ore sample. This is a full laboratory program which takes the ore sample through leaching, iron hydrolysis, aluminium precipitation and mixed hydroxide precipitation. A full series of optimisation tests will be conducted on the sample, providing the first indicative full process recoveries and by-product specifications.
An executed Non-Disclosure and Confidentiality Agreement is required before this step is undertaken.
The Full Bench Scale Testwork Program has proven effective in DNi’s experience at predicting certain aspects of pilot plant performance. The testwork proposed is based around a series of optimisation tests at small bench scale for leaching. Based on these tests, one acid addition will be selected and a bulk leach conducted to produce solution for further testing. This solution will be used for optimisation of iron hydrolysis, aluminium precipitation and mixed hydroxide precipitation.
For the leach tests we will conduct 3 kinetic tests at different acid additions (calculated based on head grade assay) on each sample. Samples will be taken every hour over a five-hour leach to provide kinetic data. Solutions and solids will be assayed and post leach solutions will be titrated for free acid. For the iron hydrolysis tests we will test the optimised leach solution, from the bulk batch leach test for one sample, at a range of temperatures to determine optimal temperature and time at temperature. For the aluminium precipitation we will test the optimised post iron hydrolysis liquor, from the bulk batch iron hydrolysis for one sample, and initially we will conduct a single stage precipitation, taking samples periodically to assess the precipitation response to MgO. This data will allow three tests to be conducted on a two stage aluminium precipitation for optimisation before the bulk batch tests. The mixed hydroxide precipitation testwork will be done similarly to the aluminium precipitation testwork. All final products will be assayed for nitrogen, to provide a preliminary nitrate balance for the sample testwork.
The Full Bench Scale Testwork Program ideally requires between 10-15 kg of representative sample – dry basis, sized 100% passing 0.5mm, however a modified program may be able to be conducted on smaller samples. DNi’s testing facility in Western Australia has access to both quarantine treatment facilities and particle size reduction facilities if needed.
Pre-feasibility study (optional)
The next phase of development of the project is often the execution of a pre-feasibility study, which should provide the information needed to evaluate if the project is economically feasible. DNi has experience developing scoping level studies, and can either develop this study in-house or work with a preferred engineering house. Some input from the client will be required during this phase, including plant capacity (or ore throughput rate) and unit costs for certain operating cost items (such as local costs for labour, mining etc.) can assist making the estimate more accurate.
The output from this study will typically consist of a conceptual flow diagram, preliminary equipment list, and an order-of-magnitude capital and operating cost estimates. Initial inputs to the mass and energy model used to generate process flows will come from the Full Bench Scale Testwork Program. Data not derived from the lab testwork will be generated from prior piloting campaigns on different ore sources.
DNi Pilot Plant Operation
The next step is to operate DNi’s pilot plant facility on the ore sample. This will generate the data needed to allow accurate design of the commercial scale plant. The pilot plant facility, located in CSIRO’s Waterford facility in Western Australia, was constructed in 2012 and operated for most of 2013. It covers the full DNi Process™ flowsheet, minus ore preparation, including leach, solid/liquid separation (CCDs), tails neutralisation and filtration, iron hydrolysis, iron product settling and filtration, aluminium precipitation, aluminium precipitate settling and filtration, mixed hydroxide precipitation (MHP), MHP settling and filtration, barren evaporation and decomposition, and acid recovery.
Ideally, the engineering group designated to conduct the feasibility study or process design development would be selected prior to start-up of the pilot plant. A strong relationship between the engineering group and the operation of the pilot plant will aid in optimum design of the commercial plant and ensure all required data is identified by the engineering group.
The pilot plant itself was designed on a nominal tonne per day throughput, and at least 30-60 tonnes of representative sample will be needed to operate the pilot plant for sufficient time to generate the required data for the next engineering work.
Process Design Development/Feasibility Study
The results from the pilot plant testwork can now be used for the design of the full-scale industrial plant. The chosen engineering firm will work with the DNi team to jointly develop a provisional layout.
A prerequisite for the development of the process design package is the signing of a Licence Agreement between DNi Technologies Pty Ltd and the client.
DNi and the engineering firm will complete the process design and the final design package for the client will include:
- Process description
- Process design criteria
- Mass and energy balance
- Equipment list and detailed equipment specifications
- Process control philosophy
The package will have sufficient information for the generation of a full bankable feasibility study.
Engineering design, construction and commissioning
When the project has been approved and the final engineering company has been selected, DNi will, as part of the service provided, work closely with the engineering firm during the full design period as well as the construction phase, to ensure the design and construction proceed according the specifications required. DNi will also assist during commissioning and training of new staff and operators.