Barren liquor

Fig. 1. Schematic flowsheet of uranium processing (acid leach and ion exchange) operation. Numbers refer to the numbers that appear in the boxes on the flowsheet. Operations (3), (6), (9), and (11) may be done by thickening or filtration. Most often, thickeners are used, followed by filters. The pH of the leach slurry <4) is elevated to reduce its corrosive effect and to improve the ion-exchange operation on the uranium liquor subsequently separated, In tile ion exchange operation (7), resin contained in closed columns is alternately loaded with uranium and then eluted. The resin adsorbs the complex anions, such as UC fSO 4-. in which the uranium is present in the leach solution. Ammonium nitrate is nsed for elution, obtained by recycling the uranium filtrate liquor after pH adjustment. Iron adsoibed with the uranium is eluted with it. Iron separation operation (8) is needed inasmuch as the iron hydroxide slurry is heavily contaminated with calcium sulfate and coprecipitated uranium salts. Therefore, the slurry is recycled to the watering stage (3). Washed solids from 1,6). the waste barren liquor from (7), and the uranium filtrate from (11) are combined. The pH is elevated to 7.5 by adding lime slurry before the mixture is pumped to the tailings disposal area. (Rio Algom Mines Limited, Toronto)...

The barren liquors from the product separation or recovery sections, and the waste disposal facility may be recycled as wash liquor to the last stage of the leach-wash system after appropriate treatment. The process may include other streams such as an inlet of lixiviant or additional wash water, and a ficticious exit stream representing losses. 

A major source of water for leaching is the normally acidic run-off water from the mining operation itself. O Leary (02) describes a technique of cleaning up to 900 gal/min of mine and tailings water at the Butte operation of the Anaconda Company. The suspended solids, which at times are in excess of 2% by weight, are equivalent to about 50 tons of mud per day. Since copper is recovered from this stream by precipitation and the barren liquor is used to leach the mine w aste dumps, solids, and colloidal materials have to be removed. With a flocculant, a 98% reduction in solid content is attained with a feed stream containing 0.22% solid. 

Conditions are not critical and the nickel catalyst can be recovered by electromagnetic separation and recycled indefinitely. The barren liquor, after removal of the uranium and vanadium oxides, can similarly be reused directly for leaching. 

Absorption through three columns in series for 5 hr at 60 gal/min until the barren liquor leaving the column contains about 1 per cent of the feed uranium concentration. This liquor may be used for pumping the extracted pulp from the leaching process to a tailings dam . 

A schematic diagram of the process is shown in Fig. 3.14. In this process, the resin is made to flow almost as liquid down a 4 ft diameter absorption column and up a 13 ft by 2-5 ft elution column. Meanwhile the leach liquor, or in this case the pulp , is pumped up the absorption column counter-current to the resin, and the eluent similarly flows down the elution column. Under suitable conditions, the ore particles remain with the barren liquor and can be pumped away from the plant with it. 

A typical analysis of the resulting uranium barren liquor is as follows ... 

Excess barren liquors must generally be treated before discharge to remove manganese by a combination of pH adjustment with lime and oxidation. 

Amine reagents also extract thorium from carbonate solutions and the use of a primary amine, RNH3C1, where R = C10 to Cl3 alkyl, as a 20% solution in kerosene allowed the concentrations of impurities in the extracted thorium to be reduced by factors of 33.8 for UVI, 111.4 for MoVI, 18.9 for Zrlv and 6167 for Mg11.177 The extracted thorium species was shown to be of the composition (RNH3)4Th(C03)4(H20)x. Di(tridecyl)amine has been used to extract thorium from barren uranium process liquors in the Blind River plant in Canada147 and flowsheets for the recovery of lanthanides, U03 and high-purity Th(S04)2 from the Elliot Lake area in Ontario using Primene/isodecanol have been described.178... 

The selective leaching of the nickel and cobalt from the gangue material is carried out in Pachuca-type leaching vessels with 98% sulfuric acid at temperatures between 450 and 500°F and with equivalent pressures between 400 and 600 psi. A typical leach liquor contains 6 gm/liter Ni, 0.6 gm/liter Co, 0.6 gm/liter Fe, 2.3 gm/liter Al, and 67 gm/liter SO4. Each batch is leached for about 90 min to extract 95% of the metal values. Preheating and heating of the ore slurry is by direct steam absorption in the reaction vessel. The barren residue is separated from the leach liquor by countercurrent decantation to a density of 55-60% solids. The solids are washed with very little dilution and about 99.5% of the soluble value are recovered. 

Stage 8 column (c) on stand-by to become column (b) in next cycle PL = pregnant liquor W = water 1 = 1st eluant 2 = 2nd eluant P = to precipitation BD = barren discharge (Reproduced by permission from Ion Exchange In Uranium Extraction , in Ion Exchange Sorption Processes In Hydrometallurgy , Critical Reports on Applied Chemistry, Vol. 19, ed. M. Streat and D. Naden, Wiley, Chichester, 1987, Ch. 1)... 

The bacteria oxidize and break up the copper minerals, the Cu(II) thus formed dissolving in the acidic liquors. The leach solution is collected at the bottom of the dump, at which stage it will contain about 2 g liter" of copper. The copper is extracted by treating the liquors with scrap iron (or by electrolysis) and the barren leach solution, which... 

Advantages of this system ate simplification of fluid valving and piping The adsorption columns need be cormected only to leach liquor supply, to barren solution disposal, and to resin transfer tank and the elution colurtms need be cormected only to eluant and wash supply, to eluate and recycle storage, and to resin transfer tank. This reduces the chance of cross contamination of solutions between the adsorption and elution systems. 

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