Our Technology
Niomet is immersed in the development of the next generation Nickel Laterite Treatment Processes for the removal of nickel and cobalt metals. The Niomet proprietary portfolio contains a suite of highly optimized and efficient metallurgical processes, designed to solve problems of HPAL for the extraction of nickel and cobalt from nickel containing lateritic deposits.
The currently-favored method for treating the high-iron limonitic laterite ores is the HPAL (High Pressure Acid Leaching) Process. Simply put, HPAL entails leaching the nickel laterite ore at high temperature and high pressure in sulfuric acid. While more than 90% of the contained nickel and cobalt are recovered, the process is mostly known to be marginally economic because it consumes large amounts of sulfuric acid, fresh water and neutralizing agents such as limestone and lime. The high acid consumption also makes it vulnerable to the world price of sulfuric acid and sulfur, which over recent years has fluctuated dramatically.
Despite being very efficient in extracting both the nickel and the cobalt at levels above 90%, conventional HPAL requires very large quantities of sulfuric acid to leach all of the desired metals. This is partly because some of the sulfuric acid contained the leach liquor does not react with any metals. In conventional HPAL, this free acid eventually heads toward the end of the process where it is treated with a neutralizing agent for disposal. However, recirculating a selective portion of the leach liquor back to the feed preparation stage, the unreacted sulfuric acid is given a ‘second chance’ (and later third, fourth…etc.) to leach targeted metals. As a consequence, the acid utilization efficiency increases therereducing the need for fresh sulfuric acid input.
During the feed preparation stage of conventional HPAL, a large amount of water needs to be added to the raw nickel laterite feed to enable efficient pumping of the feed into a pressurized leaching vessel (autoclave). More specifically, one tonne of fresh nickel laterite ore requires approximately one tonne of fresh water, which in arid areas such as Western Australia, is not always readily available. Since the leach liquor contains water, recycling a selected portion the liquor back to the feed preparation stage significant reduces the need for adding fresh water.
In conventional HPAL, a large quantity of limestone is required to neutralize the extra sulfuric acid that has not reacted with metals. Additionally, any water in the process must also eventually be treated with lime or another neutralizing agent to insure removal of base metals prior to environmental discharge.
But in the Niomet process, important quantities of acid and water are essentially being recycled which reduces their volumes throughout the final stages of the process. As a consequence, usage of neutralization agents during operations is reduced.
Nickel Sulfide Feeds
Variations of the above technology for laterites can be applied to the treatment of nickel sulfide ores. Rather than using sulfuric acid, however, in this case hydrochloric acid is used, and leaching can be carried out at atmospheric pressures rather than in an autoclave. The advantage of using chloride over sulfate or conventional smelting is that metals are much more soluble in chloride solutions, therereducing equipment size, and separation of metals is much easier. However, most importantly, the sulfur in the feed is recovered into its elemental form rather than into sulfate (as with sulfuric acid circuits) or sulfur dioxide (in the case of smelting). High recoveries of metals are possible, including recovery of the precious metals often associated with nickel sulfide ores.
The Niomet Solution
To solve the HPAL issues, Niomet Nickel recycles a selected portion of the leach liquor back to the feed preparation stage, thereoptimizing the process significantly:
High acid requirement eliminated
High fresh water input eliminated
High lime/limestone requirement eliminated
Cost Efficiencies
Operating Costs
· High recoveries of nickel and cobalt leads to higher returns
· Recycling of the leach liquor leads to lower consumption of sulfuric acid (~50%) compared to +500kg/t of acid in the conventional HPAL Process where recycling is not practiced. Acid costs are therefore reduced
· Costs associated with the requirement for fresh water for feed preparation is virtually eliminated
· Costs associated with limestone required for neutralization stages is reduced significantly
· Lower energy consumption per unit of nickel relative to HPAL
Capital Costs
· The re-cycling step yields a pregnant solution of higher nickel and cobalt concentrations into the downstream metal recovery system. As a consequence, the equipment required for that section is reduced in size (cheaper equipment occupying a smaller footprint).
· The Niomet Nickel Process is capable of treating the full laterite profile, both limonitic and/or saprolitic ores, using a single flowsheet.
Environmental Benefits
Fresh water requirement reduced to zero or absolute minimum
The quantity of process water to be disposed to the external environment is reduced
Production of saleable magnesia solves the magnesium disposal problem experienced HPAL operations.
The mass of waste residues is minimal relative to HPAL due to minimal disposal of reagent and neutralizing agents – and production of saleable co-product (Mg, Co). This is a major advantage in high-rainfall tropical environments.
Recoveries
Niomet’s unique proprietary process consistently maintains high recoveries of nickel and cobalt at over 95%.
Patents
WO/2002/050321 – ACID LEACHING OF NICKEL LATERITE ORES FOR THE EXTRACTION OF THEIR NICKEL AND COBALT VALUES
WO/2008/003160 – METAL RECOVERY SYSTEM AS APPLIED TO THE HIGH PRESSURE LEACHING OF LIMONITIC NICKEL LATERITE ORES
WO/2002/036838 – DIRECT ATMOSPHERIC LEACHING OF HIGHLY-SERPENTINIZED SAPROLITIC NICKEL LATERITE ORES WITH SULPHURIC ACID
US6379637 – Direct atmospheric leaching of highly-serpentinized saprolitic nickel laterite ores with sulphuric acid
US6391089 – Acid leaching of nickel laterite ores for the extraction of their nickel and cobalt values