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High pressure acid leaching

Interest in the hydrometallurgical treatment of nickel and cobalt-bearing ores has kept pace with demand for these commodities. Nickel laterite ore constitutes more than two thirds of the worlds known nickel resources and the production of nickel from sulphide ores is expected to slow in coming years. A major portion of the laterite reserves are not amenable to conventional pyrometallurgical treatment, which requires higher grades and larger power requirements. As such, High Pressure Acid Leaching (HPAL) is the preferred treatment option for laterite projects. The HCE can accommodate a simple amenability leach test, progressing to scoping studies on master composites, right through to bankable feasibility studies encompassing comprehensive leach optimisation, process validation and variability studies.

Autoclave Parr

Dedicated autoclave facility

In essence, HPAL involves sulphuric acid leaching of lateritic ores at temperatures above 240ºC, which can only be achieved at high pressures. The HCE has a dedicated fully equipped pressure leaching facility with a range of bench scale autoclaves including; 2 x 1 Gal Ti2 and 1 x 5 Gal Ti2, plus a 1 Gal Hastelloy batch autoclave.

A continuous submarine 6-compartment Ti. Gr. 7 autoclave 90L autoclave facility is available for circuit development and is one of the most advanced of its kind available at any independent testing facility globally. This HPAL Pilot Plant is Ti Gr.7 and has maximum operating temperature of 290ºC at 8500 kPa, variable retention: (60 – 120 min), with a single stage flash let-down system. The plant treats up to 30 kg/h solids and handles liquors with up to 70 g/L Cl- .

The integrated depth and breadth of the suite of technical services available to our experienced staff means that testwork is carried out efficiently and informed decisions can be made in a timely manner. We have access to expertise and developments at the cutting edge of metallurgical technology.

Many of the challenges involved with the design and operation of modern laterite processing plants have been overcome or at least are now better understood. Problems, such as the difficulties associated with ore variability, upgrading by beneficiation and pulp rheology, can be addressed by appropriate testwork and engineering solutions.

Following leaching, and solid/liquid separation, hydrometallurgical treatments are undertaken to generate an intermediate product, typically Mixed Ni-Co Hydroxide (MHP) or Mixed Ni-Co Sulphide (MSP). The basic steps in the HPAL – MHP and HPAL – MSP treatment processes are shown below:




 Note: There are a number of possible variations to these basic flowsheets.




The appeal of nickel laterite projects has paved the way for the development of new techniques to upgrade and recover metal values from lateritic ores. Processes such as acid heap leaching, saprolite neutralisation, and pyrometallurgical upgrading have become an important consideration for many existing and developing projects. Other more novel investigations have also gained attention such as the addition of sulphide material as a feed/reductant to HPAL circuits and the use of alternative lixiviants such as in the Direct Nickel (DNi) and Intec processes.

Don't see what you need or are unsure about some of the services and associated requirements?

We understand that metallurgical testwork is not a one size fits all or a pick off a menu proposition, and so we are happy to help walk you through the process. Or you might know exactly what you want and just need some clarifications.

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Here are some frequently asked questions

Associated testwork services

Leach testwork rarely happens in isolation and typically many other processes are required pre and post leaching testwork, as follows: Atmospheric Leaching, Neutralisation, CCD and Solution Purification, Impurity Removal, Solvent Extraction, Electrowinning, Column Heap Leaching.

Others include: Sample Characterization, Mineralogy, rheology, solid liquid separation including flocculation and settling, Iron control chemistry, tailings management, materials of construction selection testwork (corrosion coupons) preliminary piloting and fully integrated piloting

Click on the above links or contact us for further information. We can integrate a full program for you if required.