THREE YEARS' EXPEREENCE OF OPERATION
1. BRIEF HISTORY
The discovery in 1956 of a large uranium deposit in Mounana demonstrated the potential of Haut-Ogooue' and led to the creation in 1958 of the Compagnie des Mines d'Uranium de Franceville (COMUF). Production commenced in 1961 when the first plant was set up with an initial capacity of 500 t/a of metal uranium in the form of a pre-concentrate with an original grade of 32%. Average production remained at about this level until 1972 and then increased by stages from 1973, to reach a capacity of 965 t in 1976 with pre-concentrates graded as high as 50%.
This increase had been made possible by small modifications to the installations and operating conditions. In 1977 the commissioning of a solvent extraction shop enabled a further step in production and a definite improvement in the quality of the market product, which was then delivered in the form of a 75 % grade magnesium uranate. Thus, in 1979 the COMUF reached its record production of 1100 t.
In the same year it started work on a new shop capable of producing 60 t/d of sulphuric acid, intended to cope both with the previous increases and a projected 43
44 JUG
extension to 1500 t/a of metal uranium. As the original shop was stretched to the extreme limit of its capacity with installations which began to show signs of wear and tear, the decision was made in 1978 to build a new plant with a greatly increased capacity, intended to bring treatment potential to 550 000 dry t/a ore. The sulphuric acid shop started operations in January 1980 and the new plant in April 1982.
2. LOCATION
The new plant is located virtually at the geographical centre of Mounana's industrial estate. It is linked by pipe racks to the existing installations, i.e. essentially the extraction shop and acid production shop. Its raw water supply comes from a fast flowing river (the Lekedi) a few kilometres away, upon which a pumping installation with a capacity of 600 m3/h was created as part of the same project, thus enabling a supply under better conditions for the entire estate.
3. CONSTRUCTION
Work commenced in April 1980 and continued through to March 1982. The project included the following installations:
(a) A complete plant for mechanical ore preparation;
(b) A plant for acid leaching, solid-liquid separation and washing of the ore over band filters;
(c) Storage ponds for pregnant liquor coming from the filtration;
(d) A precipitation, filtration and drying shop enabling magnesium uranate to be obtained from the loaded brine coming from the solvent extraction shop;
(e) The leached ore neutralization and pumping installation;
(f) Modification of the leaching and countercurrent decantation (CCD) of the old plant for adaptation to effluent treatment;
(g) A reagent preparation shop (flocculants, magnesium oxide, lime for neutraliza-tion of the leached ore, chlorate);
(h) A pipe rack between the new plant and the existing installations, including the solvent extraction shop and sulphuric acid production shop;
(i) A raw water pumping station in a river 6 km away together with suitable storage and distribution network to enable supply to all the COMUF installations.
The capacity of these installations is 80 t/h of dry ore and 250 kg/h of metal uranium for uranate precipitation and preparation in accordance with the size chosen for the solvent extraction shop built in 1977.
The French engineering companies were entrusted with the realization of the project, one to be in charge of mechanical preparation, the infrastructure works, and the other with the chemical side of the treatment. The COMUF managed the project and ensured co-ordination between the two engineering companies.
IAEA-TC-453.5/14 45 4. CONSTRUCTION COSTS
During the course of construction, the following quantities of material and equipment were used:
Concrete 6300 m3
Structural steel 1935 t Equipment other than structural steel 2380 t
As the works carried out had to fit into an existing industrial context, their over-all cost cannot be directly compared with those of a complete new project. Indeed, certain installations indispensable to a uranium ore treatment plant (solvent extraction shop, and to a lesser degree the sulphuric acid shop) are excluded from these costs.
Similarly, reutilization and modification of existing installations, and the need to build links between plants further apart than would be the case with an entirely new unit make the comparison difficult using costs pertaining to the realization as a whole.
Consequently, we give only the costs of the workshop which more easily lend themselves to comparison, together with cost parameters enabling a possible future attempt to extend to other cases.
4.1. The costs of the workshops
The amounts are expressed in constant F.Fr.' at 1 Jan. 1979 rate, and include only the construction costs proper, i.e. without training, startup and credit expenses:
Storage of run-of-mine ore, including the rough stone base of the storage area and its drainage network
Primary crushing
Grinding, with ore spillage recovery concrete made basin (semi-autogenous grinding; supply in 0-200 mm;
product coming out at 95% minus 630 Thickening of the neutral pulp
Storage of crushed material (in metal silos of 3 x 600 t) Subtotal for mechanical preparation
Leaching, filtration
Uranate precipitation and preparation
Preparation of reagents (flocculants, magnesium oxide,
chlorate, lime for leached ore neutralization) 17 042 5
In thousands of constant French francs (F.Fr.).
4 6 JUG
Storage ponds of pregnant liquor (1 x 645 m3 + 2 X 2250 m3) with pumping station towards solvent extraction (SX) shop
located 1000 m away 5 262 Subtotal for chemical treatment excluding SX and
excluding treatment of liquid effluents (100 358) Raw water pumping station, capacity 600 m3/h with 5.5 km pipe
(300 mm 0 ) and a storage tank of 3000 m3 11 101 Leached ore separation performed on cyclones (for separating
the coarser fraction used for backfilling the mine) and
installation for hydraulic transportation to tailings 6 489 4.2. Costs per main types of expenses for the whole of the realization
These costs are exclusive of duties and taxes and have a relative value compared with the total cost of the realization.
— Equipment and other supplies, ex-works: (30.1%) Itemized equipment
Pipework, connections & fittings Electrical equipment
Instrumentation Structural steelwork
Miscellaneous, including spare parts
All works and services performed on the site:
Earth moving
Roadways & net works Concrete works
Internal works in building
General assembly (structural steel, equipment, piping, roofing
& coverings, painting) Electrical
Automatic control instruments Technical assistance by suppliers
14.53
— Packaging & transport 6.8
— Detailed engineering (detailed design, purchasing, budget control, construction supervision, startup assistance, detailed design of
concrete foundations 14.7
— Preliminary studies (grinding tests, laboratory tests, soil studies,
basic engineering) 3
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