U. SAGDIK
Mineral Research and Exploration Institute of Turkey, Dairesi, Ankara,
Turkey
Abstract
TECHNOLOGICAL STUDIES ON THE MANISA-KOPRUBA§I URANIUM ORES OF TURKEY.
At the end of the laboratory and pilot plant scale technological experiments on the uranium ores which are located in the Manisa-Koprubasi basin, three main types of ore have been classified:
(i) Kasar type: The ores consist of secondary uranium mineralization (autunite, meta-autunite and torbenite) in loosely consolidated sands, gravels and clays of Neogene Age.
Heap leaching has been carried out on 100 and 1000 t ore samples (0.05% U308) under eco-nomical conditions, such as 20 to 40 kg of H2SO4 per tonne of ore at ambient temperature;
original size —20 cm, solid/liquid ratio of 10, 20 days, and 90% recovery of uranium has been reached. The uraniferous solutions (1 to 2 g of U308 per litre) obtained from the heap leaching operations were purified in a solvent extraction unit with a capacity of 100 ltr/h by using an Alamine 336-kerosene-decanol solution. The uranium in the purified and concentrated solutions (15 g of U308 per litre) was then precipitated as a yellow cake with 65 to 75% U308 content by means of magnesia milk.
(ii) Tasharman type: No specific uranium mineral has been detected in the mineralogical determination, although uranium is disseminated in phosphate minerals as dahllite and apatite.
Uranium in the ore has been leached under rather uneconomical conditions; 100 kg of H2S04
per tonne of ore, particle size —1 cm, 25°C, 30 days. In the SX-treatment of pregnant solutions phosphate ions, higher acidity than pH 1, and compounds formed as a chemical precipitation, hindered the SX-recoveries. In such cases, the addition of acid, dilution of pregnant solutions, membrane filtration, or 40°C temperature have been applied to decrease the uranium loss in the raffinate.
(Hi) Carbonate type: Even if alkaline leaching at 65°C, or leaching with 400 kg of H2S04
per tonne of ore, was carried out on —200 mesh ore samples, no acceptable uranium recoveries were obtained.
INTRODUCTION
Technological research has been carried out on the surface-formed uranium ores explored by the Mineral Research and Exploration Institute (MTA) at the Manisa-Kopruba^i area of Turkey. In these experiments the main aim was:
(1) To determine the chemical solubility behaviour of each type of ore.
For this purpose, the ore was ground to minus 65 mesh and by applying agitating 11
ORE
leaching to these ground samples, some parameters such as, (a) selection of the best reagent, (b) amount of reagent consumed, (c) leaching time and temperature,
and (d) influence of the oxidant on the leaching process, have been investigated.
(2) To determine the optimal particle size range for which the static column technique could be used most effectively and economically.
(3) To verify the laboratory scale findings on a pilot plant scale, particularly the applicability of heap leaching.
EXPERIMENTS
Agitating leaching tests on the minus 65 mesh ores showed that there was no effect of oxidant (KC103) on the extraction of uranium. As far as the effect of temperature is concerned, with the temperatures of 65°C and ambient, no difference was achieved in the recoveries. Sulphuric acid, as a leaching reagent for uranium, was found to be superior to other reagents such as nitric acid, hydrochloric acid and sodium carbonate.
After these experiments, the possibility was studied of applying the Lixiviation Acceleree process to the ores from which uranium could be extracted with an economical amount of acid. The process has many advantages such as avoiding the necessity of grinding, agitation and filtration.
In the experiments, the ore was crushed to minus 2 cm using a jaw crusher and then 10 kg of sample was filled in a PVC column 10 cm in diameter and 1 m in height and an acid solution (1 ltr/d) was dropped on the ore by means of a dropper-pump. Each day, 1 ltr of pregnant solution filtered from the bottom of the column was then recycled in the same manner. This leaching operation went on until constant pH and EMF were reached. The washing was carried out first with a solution containing 10 to 20 g of H2S04 per litre and then with water. After leaching, pregnant solutions and residues were analysed for uranium. In the recovery calculations, uranium in the residue was taken into consideration.
As a result of laboratory experiments on the ores which are separately located in the K6priiba§i basin, three main types of ores have been classified:
(1) Kasar type
These ore deposits (located in the Kasar, £etinba§, Kayran, Topalli and Toma§a areas) consist of secondary uranium mineralization (autunite, meta-autunite and torbenite), in loosely consolidated sands, gravels, silts and clays of the Neogene Age.
The pilot plant tests of these ores [ 1 ] were started with Kasar ore. The ore samples taken by open-pit mining methods were loaded into six 24-t stalls without any size reduction, and wetted with uraniferous solution from the previous stall
followed by a wash with an acid solution, adjusted so as to consume 20 kg of H2S04 per tonne of ore, and thirdly by water. In these tests with the Kasar ores a uranium recovery above 90% was obtained, but optimum leaching time was rather long (8 weeks). It was noticed that an abundance of clays of the montmorillonite group had caused the formation of impervious layers that hindered the leaching.
To prevent the formation of such impervious layers, 100 t of ore (2.2 m high) was subjected to heap leaching under the same conditions as leaching in the stalls.
Three weeks of leaching was enough to obtain the same uranium recovery as above, 90%.
In order to investigate the effects of the size on the heap permeability, 1000 t of ore (3 m high) was leached under the same conditions. It was found that no problems of percolation rate were likely to be encountered in heap leaching of Kasar ores in the open. The heap leaching results of Kasar-type ores have been summarized in the Table.
The uraniferous solutions ( U308: 1 to 1.5 g/ltr, P2Os: 1.0 g/ltr, Fe : 3.8 g/ltr) obtained from the heap leaching operations were purified in a solvent extraction unit (four stages for extraction and two stages for stripping) with a capacity of
100 ltr/h by using 0.1 M Alamine 336-kerosene-decanol solution. The uranium in the purified and concentrated solutions (15 to 20 g of U308) was then precipitated as a yellow cake with 65 to 75% U308 content by means of magnesia milk (20 g of MgO per litre). After drying at 105°C uranium concentrates are kept in 50 kg boxes for further studies.
In the SX-experiments optimal phase flow-rates (aiming at 1 to 5 ppm U308 in the raffinate) were determined as pregnant solutions: 75 to 80 ltr/h, organic phase: 15 to 20 ltr/h and stripping solution: 4 to 5 ltr/h with a 40 g amine loss per kilogram of U308.
The technical quality of the magnesia (due to sintered particles or uncalcined carbonate) caused the yellow cakes of almost all ores to have high C02 and MgO contents, being in the order of 4.0% and 8.0% respectively.
(2) Tafharman type
These ores are located in the Ta§harman (conglomerate and tuffite) and Yardere areas. No specific uranium mineral has been detected in the mineralogical determination, although uranium is disseminated in phosphate minerals as dahllite and apatite.
Agitating and column leaching tests showed that extraction of uranium from Tasjharman ores could be increased by decreasing the particle size or increasing the amount of acid per tonne of ore. Very poor recoveries (less than 50%) of uranium were obtained in column leaching tests of Ta^harman ores (P2Os : 3.7%, C 02: 1.0%) most probably due to the formation of gypsum and Fe-P04 complexes and causing serious short circuiting.
Therefore, —1 cm and —3 cm Ta^harman ores were individually mixed with
— 5 cm Kasar ore for better percolation in the column leaching. With the — 1 cm particle size 90% uranium recoveries were obtained.
Although almost perfect percolation was observed in the heap leaching of mixed ore (Kasar/Ta§.Cong./Ta§. Tuff = 2/1/1 weight ratio) recovery of uranium from the Tajharman ores stayed at the 35% level. The reason for this was con-sidered to be the impossibility of the diffusion of the acid solutions into the original sized (—20 cm) Ta^harman ore particles in the heap. Heap leaching of Yardere ore resulted in low recovery and the problem that whether a higher acid concentration or a lower heap height (e.g. 1 m) were applied, cementation and poor percolation were observed.
In the SX-treatment of Ta^harman-type ore solutions produced by heap leaching, the following difficulties losing amine and uranium (up to 200 ppm) in the raffinate have arisen:
(i) The high acid consumption in the leaching resulted in solutions which con-tained higher amounts of other elements such as Fe: 14.8 g/ltr, P2Os: 13.3 g/ltr, Al: 12.7 g/ltr. This caused the formation of emulsion in the settling area and loss of uranium in the raffinate. The chemical analysis of the third phase, calcined at 800°C, explains the uranium loss; U308: 3.05%, Si02 : 22.1%, Fe : 15.2%, A1203 : 16.2%, P205 : 16.1%, S 04 : 8.3%, Ca : trace.
(ii) Formation of CaS04 decreased the S 04 ions in the aqueous phase and so more phosphate-uranyl complexes formed which were not selective for Alamine 336.
(iii) Acidity of pregnant solutions higher than pH 1 decreased the performance of the organic solvent.
(iv) Ambient temperatures below 10°C in winter increased the viscosity of the organic or third phase and thus separation of the phases in the SX-system became difficult.
To overcome these problems, some treatments have been applied evenly:
(i) Passing the pregnant solutions through a membrane filter before SX-operations.
(ii) Close pH control and bringing the pH to 1 by acid addition, (iii) Pre-heating of solutions to 30 to 35°C.
(iv) Dilution of pregnant solutions with water,
(v) Decreasing the flow-rates of all phases in the mixer-settler unit, (vi) Addition of more decanol in the organic phase.
As a result of this unsettled SX-treatment, lower grade yellow cake has been produced (e.g. U308 : 46.0%, C02 : 5.5%, P2Os : 2.3%, MgO : 13.8%, Moisture : 21.8%, Na20 : 4.5%) from Ta^harman-type ores.
(3) Carbonate type
There are three main locations for these ores, Kocadduz (C02 : 17.0%, CaO: 16.1%), Gordes and Tulluce. This type is characterized by high calcite and dahllite with some apatite. Acid leaching and alkaline leaching (100 kg of Na2C03 + 160 kg of NaHC03 per tonne of ore at 65°C) were carried out with
—200 mesh Kocadduz ore samples, but no acceptable uranium recoveries were obtained.
The Table gives the laboratory and pilot plant leaching test results of the K6pruba§i uranium ores.
CONCLUSION
The feasibility studies of the plant (aiming at 100 t of U308 per year as yellow cake) that will be installed in the area will start in the light of the informa
tion obtained from the pilot plant tests and from the exploration work still going on. Reasonably assured resources of uranium explored so far are estimated at 2500 t of U308 in the Koprubasi area (Kasar type: 1200 t U308; Ta§harman type: 900 t U308 ; Carbonate type : 400 t U308) .
Recent drilling in the Ecinlitas, area near the original Kasar deposit has indicated ore at a depth of 60 to 120 m which is described as unoxidized. In the primary agitating and column leaching tests of drilled ore samples (— 14 mesh), 90% uranium recovery was obtained by consumption of 40 kg of H2S04 per tonne of ore. Up to now, resources of this type of ore have been calculated as 300 t of U308 on the basis of 0.03% U308.
For Ta§harman-type ores, experimental work will go on by carrying out DAL (Dilute Acid Leaching) and TLL (Thin Layer Leaching) to fix the optimal point between particle size and acid consumption for the higher uranium recoveries.
Consequently, in the near future, a definite decision for yellow cake produc
tion plant will be determined by the results of drilling of the Ecinlita§ ore and research work on the Ta§harman ores.
REFERENCE
[1] SAGDIK, U., BILGEN, N. CIRALI, В., GONEN, N.. "Technological Pilot Plant Works on Manisa-K6priiba§i Uranium Ores", Report by M.T.A. Enstitusu Teknoloji, Dairesi, Ankara, (Dec. 1978).
DISCUSSION
R. BODU: I know from experience that it is difficult to determine accurately the yield from heap leaching. While it is possible to determine the volume of urani-ferous liquor and its concentration, it is far more difficult to determine accurately the ore concentration in the bins, either before or after leaching. How did Mr. Sagdik sample the material in the bins?
U. SAGDIK: Ore samples, about 24 t for each stall, were carried by trucks to the pilot plant. Nine shovels full of the ore were put into the stall and one shovel taken for the sample. So, for each stall, 2.4 t of ore sample were taken. By quarter-ing of this amount, almost 800 kg of sample was crushed to 1 cm by means of a jaw crusher. Then 50 kg of sample was taken by quartering to be ground into
— 65 mesh for chemical analyses. After leaching a similar procedure has been carried out during the discharging of the ore from the stall.
R. COLEMAN: What are the dimensions of the ore heaps (width, length and depth)?
U. SAGDIK: The following are the dimensions of the 100 and 1000 t heaps.
Heap(t) Width (m) Length (m) Depth (m)
100 8 7.5 2.2 1000 20 20 3.0 M. PERARNAU: The barren heap leaching liquor contains undissolved
radioactive elements, particularly radium and its descendants. This liquor enters edible plants directly; are the latter used for human consumption? It must be remembered that plants can not only absorb radioactive products, but also con-centrate them to a certain extent.
U. SAGDIK: Acid soluble radioactive elements go into barren liquors by the heap leaching process. It is believed that after 5 years rain wash a 0.5 m thickness on the top soil could be available for plants to be grown. It should also be noted that much of the study of vegetation is simply to determine whether vegetative rehabilitation is possible at all.
S. SEN: Continuing on the question by Mr. Perarnau I would like to add that there is a difference when the ore is original and after it is attacked with an acid. The soluble radioactive elements in the latter case are likely to be picked up by the plants grown on the soil. I also wish to ask whether the grade of the uranium concentrate produced by heap leaching meets the specifications required by the refinery?
U. SAGDIK: As seen in the paper, no problems have arisen from Kasar-type ores, but yellow cakes of Tasharman ores contain more MgO and C02 due to low U-content solutions (less than 10 g of U308 per litre) from SX-treatment.