Uranium from Phosphates
(Updated June 2013)
- Rock phosphate deposits contain many million tonnes of uranium, which may be extracted as a by-product of making fertilisers.
- Some 20,000 tonnes of uranium has already been obtained from these rock phosphate deposits, but the process became uneconomic in the 1990s.
- Higher uranium prices and process refinements have changed the economic situation.
In addition to the 5.4 million tonnes of uranium in known recoverable resources, there are substantial amounts comprising what is known as "unconventional resources". Chief among these is rock phosphate, or phosphorite. Estimates of the amount available range from 9 to 22 million tonnes of uranium.
About 20% of US uranium came from central Florida's phosphate deposits to the mid 1990s, as a by-product, but it then became uneconomic. From 1981 to 1992 US production averaged just over 1000 tU per year, then fell way sharply and finished in 1998. The IAEA "Red Book" also reports significant US production 1954-62. With higher uranium prices today the US resource is being examined again, as is a lower-grade one in Morocco. Plans for Florida extend only to 400 tU/yr at this stage.
Cameco and Uranium Equities Ltd are setting up a demonstration plant in the USA using a refined process – PhosEnergy – and estimate that some 7700 tU could be recovered annually as by-product from phosphate production, including 2300 tU/yr in the USA.
Phosphate rock production for fertilizer in 2010, million tonnes
|Morocco & W. Sahara
|World total in 2010
Phosphate rock (phosphorite) is a marine sedimentary rock which contains 18-40% P2O5, as well as some uranium and all its decay products, often 70 to 200 ppmU, and sometimes up to 800 ppm. The main mineral in the phosphate rock is apatite, and most commonly, fluorapatite – Ca5(PO4)3F or Ca10(PO4)6(F,OH)2. This is insoluble, so cannot directly be used as a fertiliser (unless in very acid soils) so must first be processed. This is normally in a wet process phosphoric acid (WPA) plant where it is first dissolved in sulphuric acid. About 2-4% fluorine is usually present. There are about 400 plants using this wet process worldwide, with capacity of some 50 million tonnes P2O5 per year.
Some phosphate deposits – about 4% of total known – are igneous, created by magmatic extrusion as an alkaline chimney. The main mineral is apatite, with some fluorapatite.
When phosphate rock is treated with sulphuric acid in sub stoichiometric quantity, normal superphosphate is formed. If more sulphuric acid is added, a mixture of phosphoric acid and gypsum (calcium sulphate) is obtained. After the gypsum is filtered out, the resultant phosphoric acid can be treated to recover uranium.
The basic reaction is:
Ca3(PO4)2 + 3H2SO4 + 6H2O ==> 2H3PO4 + 3CaSO4.2H2O – exothermic
An improved higher-temperature process produces hemihydrate: CaSO4.1/2H2O
Fluorides need to be controlled as gases and in effluents (HF, fluorosilicic acid) and about half the fluorine reports with the gypsum. In the process a lot of crud is generated, and this was disposed of with gypsum tailings, despite its low-level radioactivity.
After the gypsum precipitation stage, triple superphosphate is obtained by reacting the phosphoric acid with further phosphate rock. Otherwise, various ammonium phosphate fertilizers can be produced by reacting the phosphoric acid with ammonia.
The uranium is normally recovered from the phosphoric acid (H3PO4 – bearing about 28% P2O5) by some form of solvent extraction (SX). Kamorphos is developing a simpler version of this.
PhosEnergy, an ion exchange (IX) process, represents a step-change refinement of the old processes. It was announced in 2009, offering uranium recovery costs of $25-30 /lb U3O8, compared with historical costs of double this.a A demonstration plant was built in Adelaide, South Australia, and shipped to the USA to operate at a US fertilizer producer, where it was commissioned in May 2012. The test campaign with four trials on two feed sources was successful, showing recoveries of over 92% at $20-25/lb operating cost, and with Cameco very fully involved. Full evaluation of the project operation with an engineering study was reported in March 2013, and $18/lb operating cost with capital cost of $156 million for a base case 400 t/yr U3O8 plant were quoted. Cameco reaffirmed its commitment in subscribing a further $4 million.
The process involves taking 27% acid, redox reduction to ferrous iron giving oxidation of uranium, primary IX ,then recycle of acid with improved quality and a secondary IX uranium recovery being much the same as that in Cameco’s US ISL operations, so potential synergy. Bottom line of process is 95% U recovery, no radwaste, $18/lb cost, improved acid quality for main plant, $120 million bolt-on plant cost.
The next phase of PhosEnergy commercialisation is expected to be a continuous on-site demonstration scale operation at the site of an existing phosphate producer. This phase will underpin a Definitive Feasibility Study (DFS) and be the basis for a full-scale commercial facility, which might be constructed and commissioned within three years of the commencement of a DFS.
As well as the PhosEnergy project, Cameco is involved independently through Nukem with CF Industries in developing a facility to recover about 400 tU/yr from Florida phosphates.
In the USA eight plants for the recovery of uranium from phosphoric acid have been built and operated since the 1970s (six in Florida, two in Louisiana). Plants have also been built in Canada, Spain, Belgium (for Moroccan phosphate), Israel, and Taiwan.
Brazil is planning a new plant with uranium as co-product with phosphate from 0.08%U ore in igneous rock, to operate from 2012 at 1000 tU/yr. Morocco has by far the largest known resources of uranium in phosphate rock. Egypt reports 42,000 tU in phosphate rocks, at 50-200 ppm U.
The potential amount of uranium able to be recovered from WPA phosphoric acid streams is over 11,000 tonnes U per year (global P2O5 production in 2010 was 33.6 Mt). The economic benefit will be both in the value of the uranium and in reduced regulatory demands on disposal of low-level radioactive wastes arising from the WPA process. Estimated uranium production costs will put the new process in the lowest quartile of new uranium production.
Santa Quiteria and Itataia mines, Brazil
This has reserves of 340 Mt of phosphate containing 140,000 tU at Santa Quiteria and 80,000 tU at Itataia, grading 0.054% U in P2O5, giving 1270 tU/yr from about 2015, 970 tU of this from Itataia.
The country has reserves of 1400 Mt phosphates containing 170,000 tU. At 9.6 Mt/yr P2O5 production, this would yield 2300-2680 tU/yr by-product. Nukem and CF Industries were planning a 430 tU/yr uranium recovery operation at CF's Plant City.
The country has reserves of 1500 Mt phosphates containing up to 140,000 tU. At 676,000 t/yr P2O5 production the uranium potential is 135 tU/yr. The government is putting out the Qatrana phosphorites for tender to develop, containing 52 Mt phosphate and 22,000 tU with vanadium.
The country has reserves of 100 Mt phosphates containing 40,000 tU.
The country has reserves of 100 Mt phosphates containing 50,000 tU. At 1.6 Mt/yr P2O5 production, this would yield 265 tU/yr by-product.
The country has reserves of 50 billion tonnes of phosphates containing 6.9 MtU. At 4.8 Mt/yr P2O5 production, this would yield 960 tU/yr by-product. There is some expectation of 1900 tU/yr production from 2017.
a. The PhosEnergy process is being developed by Uranium Equities Limited (UEQ) through a US registered company, Urtek LLC. Cameco secured rights to earn up to a 73% interest in the technology, and initially paid $12.5 of the $16.5 million required for this to UEQ and a further $4.5 million for the founder's 10%. UEQ subsequently agreed to pay Cameco a share of that 10%, to hold 27% of the rights for the process. Cameco paid a further $4 million in March 2013 to reach 73% share. On the basis of its earlier 70% interest, Cameco agreed to provide funding for a minimum of 50% of UEQ’s portion of capital expenditure for the construction of the first commercial plant, repayable out of earnings. Cameco and UEQ are seeking to enter commercial arrangements with phosphate producers where the process would provide a technical solution for the recovery of uranium from phosphates. The capital required to install the process would be in exchange for off-take from the facility. [Back]
1. International Atomic Energy Agency, Safety Reports series No. 78, Radiation Protection And Management of NORM Residues in the Phosphate Industry (2013) [Back]
Guzman, ETR et al., Uranium in Phosphate Rock and Derivatives (1995)
WISE, Uranium recovery from phosphates