Arafura Rare Earths Ltd, page-1137

The Manufacturing and Separation Process

Nolans Bore has apatite, monazite, and allanite, in essence, 2 phosphate minerals and a form of silicate mineral. The phosphate percentage in the ore is 13% P2O5 along with 2.9% total rare earths. The predominant rare earth mineral in the ore body is apatite. The monazite tends to occur as micro inclusions within it. Higher metamorphic grades of allanite are present towards the edge of the ore body where alteration is observed. The company realised that, unlike other rare earth deposits, it cannot produce a high-grade rare earth concentrate from beneficiation.

Though the company can produce a high-grade phosphate concentrate, it would need to take the chemical route to unlock the rare earth. This led to the development of the phosphoric acid pre-leach process. This process was developed in-house and patented by the company. It allows the company to leach the phosphate out of the ore, separate the rare earth before the phosphoric acid is regenerated. The regeneration of the phosphoric acid is done once the rare earths have been removed. This allows for recycling of the chemical to leach more phosphate ore and take the excess phosphate to produce merchant-grade phosphoric acid which is a fantastic by-product. About 13%-14% of the company’s revenue comes from phosphoric acid export, as per the DFS.

The ore comes in the front end of the extraction process which is carried out through a simple single-stage flotation to produce a high-phosphate concentrate. Following this, the concentrate is leached.

The rocks here are of medium hardness and require a 150-micron grind. It is separated through an open circuit roughing flotation, the simplest kind of flotation process available.

The concentrate is leached in phosphoric acid under a controlled environment. Here, the temperature is controlled to ensure to keep certain things in the solution while also keeping other things out. Following the separation, the company takes the solids and heats them, leading to precipitation. The precipitation and bake allow the separation of rare earths. Next, the company regenerates the phosphoric acid with sulphuric acid to produce the phosphoric acid that is used in leaching. The excess leaching acid is used for cleaning up the impurities, leading to the reduction in overall water content. The resultant chemical is then shipped out through the Darwin Port to India.

The leached residue is baked by using sulphuric acid. The company doesn’t need to boil the acid at 700 degrees like other players in the market. This is because it isn’t looking to remove the excess sulphuric acid from the solution. The next process involves water leaching where everything is put into the solution and the company takes out the liquor featuring the rare earth sulphate. Next, the company puts the solution through the second part of the process which is patented. Here, the company adds a chemical that causes the rarer sulphate to precipitate without neutralising the acid.

For each ton of residue, the company mixes 1.6Mt of concentrated sulphuric acid. This leads to the formation of a paste which is then heated to 250 degrees. In the case of Linus Corporation, an acid bake is used. Here the paste is mixed and heated to 700 degrees, leading to a dry discharge from the kiln. Linus Corp. has 200-300 metre long kilns, while Arafura Resources carries out the process through a paddle dryer.

The paste is then introduced in water which allows the separation of the solids and the liquids. The solids go to tailings, while the liquid comes to precipitation. Once the rare earth sulphate is precipitated, the solids and liquids are separated. At this point, the liquified mixed acid is 10% phosphates leftover in the material along with 20% excess sulfuric acid. This acid mix is used for regenerating the phosphoric acid in the pre-leach. The excess acid is added into the bake which ends up leaching apatite and making phosphoric acid a by-product. This process is highly cost-effective and significantly reduces the company’s operating costs.

The rare earths are precipitated as hydroxide and purified through the use of magnesium and other minor chemicals to remove impurities. Next, the rare earth hydroxide is leached by using hydrochloric acid. The company carries out a differential leach where all the lanthanum, neodymium, NdPr, heavy rare earths are leached, leaving behind cerium hydroxide.

The company does not need to carry all the cerium into the solvent extraction circuit. Cerium has the biggest mass of rare earths in the circuit. It is purified mainly to recover any lost NdPr. This is because cerium isn’t worth a lot, while the NdPr production is growing worldwide. The company anticipates that the market pricing for cerium doesn’t seem to be going up in the near future. However, it has the option to produce cerium in the future, if required.

Following this, the company takes the rare earth chloride and evaporates a part of the water content. The resultant solution is then put through a very small SX circuit that helps remove the sag samarium, europium, gadolinium, and heavy rare earths. Next, the solution goes through another solvent extraction circuit that removes the NdPr which can then be precipitated out using oxalic acid and calcine off into a rare earth oxide.