CA2673608A1

CA2673608A1 - Membrane separation process for separating metal complexes of differing oxidation states

Info

Publication number: CA2673608A1
Application number: CA002673608A
Authority: CA
Inventors: Larry Lien
Original assignee: Individual
Current assignee: HW ADVANCED TECHNOLOGIES Inc
Priority date: 2006-12-27
Filing date: 2007-12-27
Publication date: 2008-11-20
Also published as: WO2008140625A1

Abstract

A semi-permeable membrane process is provided that separates metal complexes having differing oxidation states, hi one implementation, the metal in the metal complexes separated in the retentate have an oxidation number of four or higher while the metal in the metal complexes passed by the membrane has an oxidation number of three or lower.

Description

MEMBRANE SEPARATION PROCESS FOR SEPARATING METAL COMPLEXES OF
DIFFERING OXIDATION STATES
FIELD OF THE INVENTION
The invention relates generally to a semi-permeable membrane process for separating metal complexes having differing oxidation states.

BACKGROUND OF THE INVENTION
Nuclear power generators require high grade, purified uranium for generating electrical power. To recover uranium from uranium-containing ores, the uranium is first solublized by a strong acid to form a uranium-bearing pregnant leach solution. The strong acid commonly solubilizes other metals, such as nickel, copper, cobalt, and molybdenum, contained within the ore. Many techniques can be used to isolate the dissolved uranium, such as selective precipitation, electrolysis, and filtration. By way of illustration, the retentate can be pH-adjusted to pH 4 or higher using a suitable base, such as lime or limestone, and the pH-adjusted retentate is then contacted with a peroxide, such as hydrogen peroxide, to precipitate uranium as U3O8.

The uranium precipitate can then be recovered by filtration or decantation.
One filtration technique is to recover the dissolved uranium using membrane separation technology. The pregnant leach solution is passed through semi-permeable membranes, which purify and concentrate most of the dissolved uranium to form a retentate. It is desired that the other dissolved metals in the pregnant leach solution pass through the membrane to form a permeate. To effect this result, the membrane is pore sized to reject, the dissolved uranium while passing the other metals. Although the other metals will be present on a mass basis in both the retentate and permeate, the permeate is commonly of a much greater mass than the retentate.
The presence of the other metals in the retentate can be detrimental to the efficiency and/or economics of the nuclear power generation process.
Membrane technology was first utilized to recover uranium in the 1960s with the advent of cellulose acetate membranes. While the membranes separated the uranium, the cellulose acetate membrane polymer had a short service lifetime in the low pH acidic leach solutions.
Composite membranes developed in the 1970s and 1980s were more stable and robust in highly acidic, low pH environments. Membrane companies, however, did not investigate the use of these composite membranes to separate and purify uranium due to a general collapse of the nuclear power industry in the 1970s arising from public disfavor with nuclear power generation.
Public support for nuclear power generation is growing as the public becomes more concerned with greenhouse gas emissions and global warming. As public support grows for nuclear power generation, so does a need for improved uranium extraction and production.

SUMMARY OF THE INVENTION
These and other needs are met by one or more embodiments of the present invention.
The present invention is directed to a membrane separation process for separating higher oxidation from lower oxidation state complexes or ionic components thereof, particularly metals and metal complexes.

In one embodiment, a method for recovering a target metal complex from one or more non-target metal complexes is provided that includes the steps:
(a) providing a pregnant solution comprising a target metal complex, lixiviant, and non-target metal complex, wherein the target metal has an oxidation state of at least about four while the non-target metal has an oxidation state of no more than about 3;
(b) providing a semi-permeable membrane capable of rejecting most, if not all, of the target metal complex while passing most, if not all, of the non-target metal complex and/or most, if not all, of the lixiviant; and (c) contacting the pregnant solution with the semi-permeable membrane to produce a retentate and permeate. The retentate includes most, if not all, of the target metal complex in the pregnant solution, and the permeate most, if not all, of the non-target metal complex and/or lixiviant.

The metals that can be separated by this process are any suitable metals having differing oxidation states, with uranium, iron, copper, cobalt, lead, silver, bismuth, titanium, magnesium, calcium, vanadium, and mixtures thereof being preferred. The process is particularly useful for recovery of uranium from a uranium ore where the uranium occurs in the presence of one or more other metals, such as silver, copper, cobalt, nickel, lead, bismuth, iron, calcium, vanadium, and mixtures thereof. These metals that can decrease the utility and/or value of the recovered uranium.

The lixiviant can be any acid or base, mineral and organic acids being preferred. In a preferred process configuration, the lixiviant is hydrochloric, nitric, sulfuric, citric, acetic acids, and mixtures thereof being preferred. Preferably, the concentration of acid can range from about 0.1 to about 30 wt%.

The lixiviant can be recovered in the permeate and reused to leach additional metal(s).
Re-using the recovered lixiviant can improve the economics of the separation process, as for example, decreasing the amount of lixiviant purchased per ton of metal recovered and/or decreasing the cost of lixiviant disposal.

The membrane can be any suitable membrane, with a semi-permeable membrane being preferred. More preferably, a membrane is close to the upper end of the reverse osmosis pore

2 size range, which can therefore resemble a leaky reverse osmosis membrane.
Preferably, the average pore size can range form about 8 to 17 Angstroms. In one configuration, the membrane has an average pore size of about 10 Angstroms. In another configuration, the membrane has an average pore size of about 13 Angstroms. In one configuration, the membrane has a pore size distribution where at least about 80% of the pores range in size from about 13 to about 17 Angstroms. In another configuration, the membrane has a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms.
To concentrate the non-target metal complex and/or the lixiviant in the permeate, the permeate can be passed through a hyperfilter or reverse osmosis membrane.
The membrane can be selected to withstand acidic environments, particularly acidic environments having a pH value of pH 1 or less. Suitable membranes can comprise polyamides, nylon, sulfonamide, and copolymers thereof.

The membrane separation can be effective. In a typical implementation, the membrane can reject from about 80 to about 99% of the target metal complex and more preferably form 90 to about 99%. The permeate can be formed when the membrane passes a substantial portion of one or more of the other metals and/or lixiviant. Preferably, the membrane can pass form about 80 to about 99% of the one or more other metals and/or lixiviant and more preferably about 90 to about 99%.

These and other advantages will be apparent from the disclosure of the invention(s) contained herein.

As used herein, " at least one", "one or more", and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions "at least one of A, B and C", "at least one of A, B, or C", "one or more of A, B, and C", "one or more of A, B, or C" and "A, B, and/or C" means A alone, B alone, C alone, A
and B together, A
and C together, B and C together, or A, B and C together.
It is to be noted that the term "a" or "an" entity refers to one or more of that entity. As such, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and "having" can be used interchangeably. The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 depicts a membrane separation process according to an embodiment of the present invention;

3 Fig.2 depicts another membrane separation process according to another embodiment of the present invention;

Fig. 3 depicts yet another membrane separation process according to another embodiment of the present invention;

Fig. 4 depicts still yet another membrane separation process according to another embodiment of the present invention; and Fig. 5 depicts yet another membrane separation process according to another embodiment of the present invention.

DETAILED DESCRIPTION
Fig. 1 depicts a process according to a first embodiment for separating a target metal complex from other metal complex(es). The metal complexes are typically in the form of coordination compounds. A coordination compound is formed by the union of a metal ion (such as a transition metal) with a non-metallic ion or molecule called a ligand or complexing agent.
The ligand may be either positively or negatively charged (such as chlorine C1-or NH2NH3+) or it may be a molecule of water or ammonia. The total number of bonds linking the metal to the ligand is called its coordination number. It is usually 2, 4, or 6 and often depends on the type of ligand involved.

In step 101, a pregnant leach solution 103 containing the target metal complex is formed by contacting a strong acidic or alkaline lixiviant with a metal-containing material, in a suitable containment such as a vat or impermeable leach pad. The pregnant leach solution 103 includes the leaching agent and dissolved metal complexes, including the target metal complex. In one configuration, the target metal is a lanthanide or actinide series metal. More commonly, the target metal is an actinide series metal, and even more commonly, the target metal is uranium.
The metal ion in the other metal complexes in the pregnant leach solution can be any metal, such as an s-block alkali metal (periodic table group 1A) or alkaline earth metal (periodic table group 2A), a d-block transition metal (periodic table groups 1B-8B), and/or an inner transition f-block metal other than uranium. The other metal complex(es) can also be a non-metal, such as a chemical containing an element of the 3A-8A group of the periodic table. In an even more preferred embodiment, the associated species is one or more of hydrogen, sodium, lithium, magnesium, calcium, barium, chromium, molybdenum, tungsten, manganese, iron, lead, bismuth, titanium, vanadium, potassium, phosphorous, fluorine, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, mercury, or a mixture thereof.

4

5 PCT/US2007/088958 The leaching agent can be any mineral or organic acid or alkaline agent capable of solublizing the target metal. Monoprotic and diprotic acids are preferred. The acid is commonly one of a mineral acid, organic acid, or mixture thereof. Preferably, the mineral acid is an acid of group 7A (halogens) or an oxide of group 3A-6A of the periodic table, such as, but not limited to, hydrochloride, hydrofluoric, hydrobromic, boric, nitric, sulfuric, phosphoric, acetic, oxalic, citric, benzoic, and mixtures thereof. Even more preferably, the mineral acid is one of hydrochloride, nitric, and sulfuric acids. Preferred organic acids are acetic, oxalic, citric, and benzoic acids.

The target metal complex comprises a metal cation of the target metal having an oxidation state or number of four or more and any associated coordinated and/or bonded chemical entities, such as ligands or complexing agents. The target metal cation can be coordinated and/or bonded with other chemicals. The chemical bond can be labile or substantially non-labile. A labile bond is a low energy bond that can be easily broken. A non-labile bond is more difficult to break than a labile bond and requires a substantial amount of energy to be broken. Examples of chemicals that the target metal cation can coordinate and/or form a covalent bond with are electron donors and/or Lewis acids, such as halides, nitrates, and other anions. The target metal cation can also form an ionic complex with one or more anions.
The one or more anions complexed with the target metal cation are commonly coordinated and/or bonded to the target metal complex. The associated coordinated and/or bonded chemical entities normally have valences, the absolute values of which is less than the valence of the metal cation. Thus, to provide valance-balanced complex the metal cation will commonly be bonded or complexed with multiple anions.
In one configuration, the target metal complex is a uranium complex. In this configuration, the uranium in the target uranium complex commonly has an oxidation state of four, five and/or six. Typically, the uranium coordinates with the anion of the leaching acid. As for example, when uranium is leached with sulfuric acid the uranium will, commonly, coordinate with the sulfate anion to form a uranyl sulfate complex. Other illustrative uranyl complexes include uranyl chloride (hydrochloric acid), uranyl nitrate (nitric acid), and uranyl phosphate (phosphoric acid).

The pregnant leach solution 103 composition depends on the application.
Typically, the pregnant solution has a pH of no more than about pH 5 and even more typically ranging from about pH -3 to about pH 3. The concentration of the uranyl complex typically is at least about 4 g/L and even more typically ranges from about 1 to about 200 g/L, and the concentration of other metal complexes typically ranges from about 0.1 to about 10 g/L. The molar concentration of uranium is at least about 0.01 moles uranium per liter and even more typically ranges from about 0.002 to about 0.5 moles uranium per liter, and the molar concentration of the other metal complexes typically ranges from about 0.0001 to about 0.03 moles of other metal per liter.
In general, the greater the atomic number of the target metal the larger the size of the target metal cation. It can be appreciated that, the atomic number of uranium is greater than the atomic number of the alkali, alkaline earths and transition metals and, therefore, uranium is typically larger in size than such other metals and, for a given atomic number, the larger the cationic charge the smaller the cation. Accordingly, a 4+ uranium cation is normally greater in size than a 6+ uranium cation. The coordinated chemical entities form an outer shell around the uranium cation. The larger the size and/or greater the number of the coordinated chemical entities, the thicker the shell around the uranium cation and the greater the size of the uranium complex.

The other metal complexes typically have oxidation states or numbers of less than four.
As in the case of the target metal complex, the other metal complexes can also coordinate and/or bond with other chemical entities. When the target metal complex is uranium, the other metal complex(es) is/are substantially more likely to be smaller in molecular size than the uranium complex.

In step 105, the pregnant leach solution 103 comprising the solublized target metal complex, any other metal complex(es), and any particulate matter, can be optionally filtered to remove at least most of any undissolved particulate matter. The particulate matter can be not only solid particles but also a solid and/or organic liquid or emulsion suspended and/or entrained within the pregnant leach solution 103. Typically, the particulate filter 105 is a microfilter and/or ultrafilter.

After filtering step 105, the pregnant leach solution 103 is supplied to a membrane cell 107 having a semi-permeable, thin film, composite membrane 110. The semi-permeable membrane 110 has a smaller pore size than the particulate filter 105.
Preferably, the semi-permeable membrane 110 is stable at pH values of about pH
5 or less, more preferably at pH values of about pH 1 or less. Or, stated another way, the semi-permeable membrane 110 is preferably stable in acid concentrations that range from about 0.1 to about 30 wt% acid. The semi-permeable membrane 110 can also withstand filtration pressures ranging from about 100 to about 1,500 psi (pounds per square inch), and even more preferably from about 400 to about 1000 psi. Non-limiting examples of semi-permeable membrane compositions having substantially sufficient pH and pressure stabilities are membranes

6 comprising polyamide, sulfonamid6, nylon, and copolymers thereof. The semi-permeable membrane is also stable at temperatures ranging from about 5 to about 95 C.
The semi-permeable membrane 110 has a pore size distribution and average pore size for effectively separating the target metal complex from the other metal complex(es). Preferably, the semi-permeable membrane 110 pore size is selected to reject metal complexes having oxidation states of four or more while passing metal complexes having oxidation states of three or less. Typically, the pore size of the membrane 110 ranges from about 5 to about 20 Angstroms or from about 90 to about 120 MWCO. Or, stated another way, the pore size and pore size distribution of the semi-permeable membrane can support an average flux ranging from about 2 to about 35 gallons per square foot per day (GFD).

In a more preferred configuration, the membrane 110 is pore-size selected to be closer to the upper end of the reverse osmosis pore size range and therefore resembles a leaky reverse osmosis membrane. When the average pore size ranges from about 8 to about 12 Angstroms and more commonly is about 10 Angstroms, the semi-permeable membrane 110 is referred to as a "tight" semi-permeable, nanofiltration membrane or "loose" reverse osmosis membrane. The tight semi-permeable, nanofiltration membrane, typically, has a pore size distribution where at least about 80% of the pores range from about 8 to about 12 Angstroms. When the average pore size ranges from about 13 to about 17 Angstroms or more commonly is about 15 Angstroms, the semi-permeable membrane 110 is referred to as "loose" nanofiltration membrane.
The loose manofiltration membrane, typically, has a pore size distribution, where at least about 80% of the pores range in size from about 13 to about 17 Angstroms.
The semi-permeable, thin-film, composite membrane 110 commonly has a thickness ranging from about 1,000 to about 3,000 Angstroms.
The membrane can have any suitable configuration. Preferably, the membrane 110 is one of a spiral wound, hollow fiber, plate and frame, and other cross-flow-type membrane. The semi-permeable membrane 110 can be tubular or plate and frame mounted or spirally wound within the membrane cell 107. Preferably, the semi-permeable membrane 110 is spirally wound. When spirally wound, the semi-permeable membrane 110 configuration can have a greater membrane surface area for separating the target metal complex.
The pregnant leach solution 103 containing the target metal complex and other metal complex(es) is supplied to the membrane cell 107 at a temperature ranging from about 5 to about 95 C and a pressure ranging from at least about 100 to at most about 1,500 psi. The average pore size of the semi-permeable membrane 110 is commonly sufficiently small that the average size of the target metal complex is greater than the average pore size of the semi-

7 permeable membrane 110. Additionally, the average pore size of the semi-permeable membrane 110 is commonly sufficiently large that the average size of the other metal complex is smaller than the average pore size of the semi-permeable membrane 110. Or, stated another way, the average pore size of the semi-permeable membrane 110 is sufficient to large to allow the other metal complex(es) to pass through, but is sufficiently small not to allow, or exclude, the target metal complex from passing through.

In one preferred embodiment, the target metal complex is a uranyl complex. The semi-permeable membrane 110 preferably rejects from about 80 to about 99% of the uranyl complex.
Even more preferably, the semi-permeable membrane 110 rejects from about 90 to about 99% of the uranyl complex. Or, stated another way, the average pore size of the semi-permeable membrane 110 is preferably sufficiently small that the membrane pores do not transmit from about 80 to about 99% of the uranyl complex. Preferably, the average pore size of the semi-permeable membrane is sufficiently small that the membrane pores do not transmit from about 90 to about 99% of the uranyl complex The membrane 110 rejects most, and preferably at least about 80%, of the uranyl complexes in the pregnant leach solution 103. The rejection of the uranyl complexes by the semi-permeable membrane 110 forms a retentate solution 111 having a uranyl concentration preferably greater than the uranyl concentrations of the pregnant leach solution 103 and permeate 109. The uranium content of the retentate 111 preferably is at least about 80%
of the uranium concentration of the pregnant leach solution 103 and at least about 20% of the uranium concentration in the permeate 111. In one application, the uranium content of the retentate 111 ranges from about 0.1 wt% to about 35 wt% uranium and even more typically from about 4 wt%
to about 35 wt% uranium. The maximum uranium content of the retentate l 11 depends, of course, on the osmotic pressure of the retentate 111.
In another preferred configuration, the other complex(es) are one or more of a metal complex and leaching agent. The semi-permeable membrane 110 transmits in the permeate 109 from about 80 to about 99% of the dissolved metal complexes and/or leaching agent having oxidation states of three or less. Even more preferably, the semi-permeable membrane 110 transmits from about 90 to about 99% of such metal complexes and/or leaching agents. Or, stated another way, the average pore size of the semi-permeable membrane 110 is sufficiently large that the membrane pores allow from about 80 to about 99% of such metal complexes and/or leaching agents to pass through into the permeate 109. Preferably, the average pore size of the semi-permeable membrane is sufficiently large that the membrane pores allow from about 90

8 to about 99% of such metal complexes and/or leaching agents to pass through into the permeate 109.

The transmission of the lower oxidation state metal complex(es) by the semi-permeable membrane 110 forms a permeate solution 109 that, assuming a homogeneous mixture in the pregnant leach solution 103, has concentrations of such complex(es) substantially the same or greater than the concentrations of the metal complex(es) in the pregnant leach solution 103 and in the retentate 111. The substantial equality in the concentrations of the permeate and retentate is due to the distribution of lower oxidation state complexes based on mass.
Because the mass of the permeate is preferably at least about 80% and even more preferably at least about 95% of the mass of the pregnant leach solution 103, typically at least most, and even more typically at least about 80% of lower oxidation state metal complex(es) are contained in the permeate 109. For example, when the lower oxidation state metal complex includes nickel, at least most, and more typically at least about 80%, of the nickel complex is in the permeate 109 due to the greater mass of the permeate 109 when compared to the mass of the retentate 111. Typically, the nickel content of the permeate 109 ranges from about 0.01 to about 15 wt% and even more typically from about 1 to about 10 wt% nickel. The maximum lower oxidation state complex content of the permeate 109 depends, of course, on the osmotic pressure of the permeate solution 109.
While a single membrane cell 107 can separate the target metal complex from the other metal complex(es), replacing the single membrane cell with one or more banks of cells, as depicted in Fig. 2, allows for larger processing volumes and flows, greater processing speed, and/or higher levels of purification.

The single processing membrane cell 107 of Fig. 1 is replaced in Fig. 2 with a membrane cell system 210 comprising a plurality of first, second, . . . xth membrane banks 210a,.,X. As will be appreciated, "x" can be any suitable number based on the application.
Typically, x will be "3" to provide three membrane banks or "4" to provide four membrane banks.
Within each membrane bank 210a,,.,,, the membranes 107 in each cell bank are arranged in parallel. For example, the first membrane bank 210a has n cells 107 arranged in parallel.
Compared to the preceding cell bank, each successive membrane bank has the same number, or more typically, fewer membrane cells 107 arranged in parallel. By way of illustration, the first, second, . . . xth membrane banks 210a,,,~ typically form a type of "funnel", with the first bank 210a having the largest number of membrane cells 107 in parallel, the second bank 210b having fewer membrane cells 107 than the first bank 210a and more membrane cells 107 than the xth bank 201, and the xth membrane bank 210, having fewer membrane cells 107 than each of the first and second banks 210a-b.

9 The first, second, ... xtn membrane banks 210a...,t are arranged in series.
That is, the second membrane bank 210b follows the first membrane bank 210a, and the xth membrane bank 210, follows the second membrane bank 210b.

The sequential decrease in bank size is due to the decreasing volume of the retentate flows handled by each successive cell bank. Although Fig. 2 shows the retentate of an upstream bank being the feed to the next downstream bank and the permeate from each bank being collected, it is understood that, in some applications, the permeate may be fed to the next downstream bank, with the retentate from each bank being collected.
The first membrane bank 210a is supplied with the pregnant leach solution 103 by a header piping system 220a. Each membrane cell 107 of the first membrane bank 210a is supplied with the pregnant leach solution 103 as described above. The target metal complex and the lower oxidation state metal complex(es) within the pregnant leach solution 103 are separated within each membrane cell 107 in the first membrane bank 210a by the respective semi-permeable membrane 110 as described above. Each membrane cell 107 of the first bank 210a generates a first retentate and permeate. A second header piping system 220b collects the first retentates of each membrane cell in the first membrane bank 210a and supplies the collected first permeates, as a first retentate solution, to a second membrane bank 210b. In a similar manner, the first permeates of each membrane cell comprising membrane bank 2 10" are collected by permeate header system 230. The first permeate of cell bank 210a has a lower concentration of the target metal complex than the pregnant leach solution 103 and an equal and/or higher concentration of the lower oxidation state metal complex(es) than the pregnant leach solution 103. And, the first retentate solution has a greater concentration of the target metal complex than the pregnant leach solution 103 and an equal and/or smaller concentration of the lower oxidation state metal complex(es) than the pregnant leach solution.

Each membrane cell 107 of the second membrane bank 210b is supplied with the first retentate solution. The target metal complex and the lower oxidation state metal complex(es) within the first retentate solution are separated within each membrane cell 107 in the second membrane bank 210b by the respective semi-permeable membrane 110. The number of membrane cells 107 in the second bank 210b is less than or equal to the number of membrane cells 107 in first bank 210a. Each membrane cell 107 of the second bank 210b generates a second retentate and a second permeate. The second retentates are collected by and supplied to a third membrane bank 210, by a third header piping system 220c. The collected second retentates forming a second retentate solution. The second retentate solution has a greater concentration of the target metal complex and an equal and/or smaller concentration of the lower oxidation state metal complex(es) than the first retentate solution. In a similar manner, the second permeates are collected by permeate header system 230. The second permeate has a lower concentration of the target metal complex than the first retentate and an equal and/or higher concentration of the lower oxidation metal state complex(es) than first permeate solution.
The process is continued until; the xth membrane bank 210,, is supplied with the x-1 retentate solution. The target metal complex and the lower oxidation state metal complex(es) within the x-1 retentate solution are further separated within each membrane cell 107 comprising membrane bank 210,, by the semi-permeable membrane 110. The number of membrane cells 107 in the xth cell bank 210X is less than or equal to the number of membrane cells 107 in immediately preceding cell bank 210,c_1. Each membrane cell 107 of xth bank 210, generates an x`t' retentate and an xth permeate. A header piping system 240 collects the xth retentates of each membrane cell in the xth membrane bank 210,, forming an x`h retentate solution. The xth retentate solution has a greater concentration of the target metal complex and an equal and/or smaller concentration of the lower oxidation state metal complex(es) than the x-1 retentate solution. The xth permeates of each membrane cell in membrane bank 210" are collected by the permeate header system 230. The x'n permeate has a lower concentration of the target metal complex than the x-1 retentate and an equal and/or higher concentration of the lower oxidation state metal complex(es) than x-1 permeate solution.
It is apparent that each successive cell bank further concentrates and purifies the target metal complex.

The retentate and/or permeate solutions of each membrane bank can be separately processed to recover the target metal and/or lower oxidation state metal complex(es). Or, the retentate and/or permeate solutions of each membrane bank can be further processed by one or more up-stream membrane banks; that is, the retentate and/or permeate solution of the ith membrane bank is further processed one or more nth membrane banks, where i<n<x.
Fig. 3 depicts a three-pass process for producing high uranium and sulfuric acid concentrates. The process configuration of Fig. 3 is not intended to be exhaustive or to limit the invention to the precise form disclosed in the following detailed description.
Rather, the process configuration was chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
A pregnant leach solution 303 comprising uranium sulfate and sulfuric acid is formed by a sulfuric acid leach of a material containing uranium predominantly in the form U308. The pregnant leach solution 303 has a uranium concentration preferably ranging from about 1 to about 330 g/L and even more preferably about 330 g/L and a sulfuric acid concentration preferably ranging from about 1 to about 320 g/L and even more preferably about 320 g/L. The pregnant leach solution 303 is supplied at a rate typically ranging from about 5 to about 50 cubic meters per hour and even more typically of about 17 cubic meters per hour to a first membrane separation cell 318 at a pressure ranging from about 100 to about 1,500 psi, and a temperature of at least about 5 to at most about 95 C. The first membrane ce11318 has a semi-permeable, thin film, composite membrane 310. The semi-permeable membrane 310 is substantially stable in sulfuric acid concentrations ranging from about 0.1 to about 30 wt% H2SO4 and/or having a pH
value of about pH 1 or less. Preferably, the semi-permeable membrane is comprised of a polyamide, sulfonamide, nylon, or copolymer thereof.
Additionally, the semi-permeable membrane 310 has a pore size distribution and average pore size for effectively separating the uranium sulfate complex from the associated sulfuric acid. Preferably, the first semi-permeable membrane 310 is a "loose"
nanofiltration membrane.
The average pore size is sufficiently small and the pore size distribution is sufficiently narrow to effectively and efficiently exclude the uranium complex from passing through the pores of the first semi-permeable membrane 310, while allowing the sulfuric acid to pass through the pores of the first membrane 310 to form a first permeate 315. Or, in other words, the first semi-permeable membrane 310 fractionates the uranium from the sulfuric acid, concentrating the uranium in a first retentate 317. The uranium sulfate concentrate of the first retentate 317 preferably ranges from about 1 to about 390 g/L and more preferably is about 390 g/L or preferably from about 1 to about 10 and more preferably about 1.7 times the concentrated of uranium in the pregnant leach solution 303. The sulfuric acid concentration in the first retentate 317 preferably ranges from about 0.01 to about 300 g/L and more preferably is about 300 g/L, or preferably from about 0.8 to about 1.2 and more preferably is about 0.9 the sulfuric concentration in the pregnant leach solution 303. The uranium concentration of the first permeate 315 preferably ranges from about 0.2 to about 180 g/L and more preferably is about 180 g/L, or preferably from about 0.15 to about 0.95 and more preferably about 0.8 the uranium concentration of the pregnant leach solution 303. The sulfuric acid concentration of the first permeate 315 is approximately equal to sulfuric acid concentration of the leach solution 303. The first permeate production rate preferably ranges from about 5 to about 20 and more preferably is about 12 cubic meters per hour. All or a portion of the first retentate 317 is returned to the feed to the first cel1308.

The first permeate 315 is supplied to a second membrane separation ce11328 at a preferred pressure ranging from about 100 to about 1,500 psi, and a temperature preferably of at least about 5 and at most about 95 C. The semi-permeable membrane 321 is substantially the same as first semi-permeable membrane 310. The uranium concentrate of the second retentate 327 preferably ranges from about 1 to about 300 g/L and more preferably is about 270 g/L or preferably from about 1 to about 5 and more preferably about 1.5 times the concentrated of uranium in the first permeate 315. The production rate of the second retentate 327 preferably ranges from about 1 to about 10 and more preferably is about 3 cubic meters per hour. The second retentate 327 is supplied to the feed to the first ce11318. The sulfuric acid concentration in the second retentate 327 preferably ranges from about 1 to about 320 g/L
and more preferably is about 320 g/L and preferably is about equal to the sulfuric acid concentration in the first permeate 315. The uranium concentration of the second permeate 325 preferably ranges from about 1 to about 130 and more preferably is about 130 g/L, or preferably from about 0.1 to about

10 and more preferably about 0.7 the uranium concentration of the first permeate 315. The sulfuric acid concentration of the second permeate 325 is about equal to sulfuric acid concentration of the first permeate 315. The second permeate 325 is produced at a rate preferably ranging from about 5 to about 15 and more preferably of about 9 cubic meters per hour. As in the case of the first retentate 317, all or a portion of the second retentate 327 is returned to the feed to the first ce11308.

The third membrane cell 338 has a membrane 330, which differs from than the first 310 and second 320 semi-permeable membranes in pore size and pore size distribution, with the other physical and chemical properties of the third membrane 330 being substantially equivalent to the first 310 and second 320 semi-permeable membranes. The third semi-permeable membrane 330 has a tight nanofiltration membrane configuration.
The second permeate 325 is supplied to the third membrane cell 338 at a preferred production rate ranging from about 5 to about 15 and more preferably of about 9 cubic meters per hour at a pressure ranging from about 100 to about 1,500 psi, and a temperature ranging from about 5 to about 95 C. The uranium concentrate of the third retentate 337 preferably ranges from about 10 to about 250 g/L and more preferably is about 230 g/L or preferably ranges from about 1 to about 5 and more preferably is about 1.8 times the concentrated of uranium in the second permeate 325. The third retentate 337 is produced at rate typically ranging from about 2 to about 10 and more typically of about 5 cubic meters per hour. All or a portion of the third retentate 337 is returned to the first membrane ce11308. The sulfuric acid concentration in the third retentate 337 preferably ranges from about 4 to about 320 g/L and more preferably is about 320 g/L. The uranium concentration of the third permeate 335 preferably ranges from about 1 to about 10 g/L and more preferably is about 10 g/L, or preferably ranges from about 0.01 to about 0.1 and more preferably is about 0.07 the uranium concentration of the second permeate 325.

The sulfuric acid concentration of the third permeate 335 is about equal to sulfuric acid concentration of the second permeate 325. The third permeate 335 is produced at a rate typically ranging from about 2 to about 6 and more typically of about 4 cubic meters per hour. The sulfuric acid of the third permeate can be recycled to the leaching step (not shown).
This process configuration shows that the series use of loose and tight nanofiltration membranes can provide benefits. The loose nanofiltration membranes are used to handle greater volumes of the pregnant leach solution and produce the first retentate 317 having a substantial fraction of the dissolved target metal in the pregnant leach solution. The second membrane cell 328 produces the second retentate, which is recycled to the first membrane cell 308 to provide a more concentrated and smaller volume first retentate 317. The tighter nanofiltration membrane treats the second permeate 325, which contains less than most, and typically no more than about 0.02%, of the target metal complex in the pregnant leach solution 303, and rejects a higher percentage of the target metal complexes than the loose nanofiltration membranes to form the third retentate 337.

Fig. 4 depicts a process configuration for recovering uranium and a lower oxidation state metal, particularly nickel, from a mineral ore. The process also provides for recovery and re-use of a lixiviant 410. This process configuration is not intended to be exhaustive or to limit the invention to the precise form disclosed in the following detailed description.
Rather, the embodiment was chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
The lixiviant 410 can be any acid, with a monoprotic acid being preferred.
Preferably, the lixiviant 410 is hydrochloric acid. In step 420 the acid solublizes the uranium and nickel from uranium-containing material, to form a pregnant leach solution 430. When the lixiviant is hydrochloric acid, the pregnant leach solution comprises hydrochloric acid and nickel and uranyl chloride.

The pregnant leach solution 403 has a pH typically of from about pH 1 to about pH 2.5, a uranium chloride concentration typically ranging from about 0.01 to about 10 g/L and more typically of about 0.05 g/L and a nickel chloride concentration typically ranging from about 0.01 to about 10 g/L and more typically of about 0.5 g/L. The pregnant leach solution 403 has a molar concentration of uranium metal which typically ranges from about 2x10"5 to about 3x10"2 moles uranium per liter and a molar concentration of nickel which typically ranges from about 6x10-5 to about 8x10-2 moles nickel per liter. The pregnant leach solution 403 is supplied at a rate commonly ranging from about 5 to about 50 cubic meters per hour to a first membrane separation cell 445 at a pressure ranging from about 100 to about 1000 psi.

The first and second membrane cells 445 and 455 each has a first semi-permeable, thin film, composite membrane 440. The semi-permeable membranes are substantially acid resistant.
Additionally, the first semi-permeable membrane 440 has a pore size distribution and average pore size for effectively separating the uranyl complex from the nickel complex. Preferably, the first semi-permeable membrane 440 is configured as loose nanofiltration membrane. So configured, the average pore size is sufficiently small and the pore size distribution sufficiently narrow to effectively and efficiently exclude the uranyl complex from passing through the pores of the first membrane, while allowing the nickel complex to pass through the membrane. Or, in other words, the first semi-permeable membrane 440 fractionates the uranyl and nickel complexes, thereby concentrating the uranium in retentate and the nickel in permeate fractions.
The uranium concentrate in the first retentate 448 commonly ranges from about 0.01 to -about 4 g/L (or, ranges from about 2x10-5 to about 1x10-2 moles U/L) and more commonly is about 0.2 grams of uranium per liter or commonly ranges from about 2 to about 10 and more commonly is about 4 times the concentration of uranium in the pregnant leach solution 430, and the nickel concentration in the first retentate 448 is commonly ranges from about 0.01 to about 5 g/L (or, ranges from about 6x10"5 to about 4x10-2 moles Ni/L) or more commonly is reduced from 0.5 grams per liter to about 0.4 grams per liter, a factor of about 0.8.
The first retentate is produced at a rate commonly ranging from about 1 to about 10 and more commonly of about 5 cubic meters per hour. The nickel concentration in the first permeate 446 commonly ranges from about 0.01 to about 5 g/L (or, form about 6x10-5 to about 4x10"2 moles Ni/L) and more commonly is about 0.6 grams of nickel per liter or commonly ranges from about 0.9 to about 1.5 and more commonly is about 1.2 times the nickel concentration of the pregnant leach solution 430, and the uranium concentration in the first permeate 446 is more commonly reduced from 0.05 grams per liter to about .01 grams per liter, a reduction factor of about 0.2.
The first permeate 446 is supplied to a second membrane ce11455 at its production rate of typically from about 5 to about 50 cubic meters per hour at a pressure typically ranging from about 100 to about 1000 psi. The uranium concentrate of the second retentate 458 commonly ranges from about 0.01 to about 4 g/L or commonly from about 0.9 (or, from about 2x10"5 to about 1x10"2 moles U/L) to about 1.1 times the concentration of uranium in the first permeate 446, and the nickel concentration in the second retentate 458 is reduced by from about 0.01 to 4 g/L (or, from about 6x10-5 to about 3x10-2 moles Ni/L) to from about 0.005 to about 3 g/L (or, from about 3x10-5 to about 2x10-2 moles Ni/L), a factor of about 0.8. The production rate of the second retentate 327 typically ranges from about 5 to about 20 cubic meters per hour. The second permeate 456 is commonly produced at a rate of from about 1 to about 40 cubic meters per hour. The nickel concentration in the second permeate 456 preferably ranges from about 0.01 to about 4.1 g/L and more preferably is about 0.7 grams of nickel per liter or about 1.2 times the nickel concentration of the first permeate solution 446. In one implementation, the uranium concentration in the second permeate 456 is reduced from about 0.01 grams per liter to about .002 grams per liter, a reduction factor of about 0.2.
The third semi-permeable membrane ce11465 has a third membrane 460 which differs from than the first and second semi-permeable membranes 440 in pore size and pore size distribution, the other physical and chemical properties of the third membrane 460 being substantially equivalent to the first and second semi-permeable membranes 440.
The third membrane 460 is a reverse osmosis membrane preferably having an average pore size of about no more than 10 Angstroms and more preferably less than 8 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 5 to about 10 Angstroms. Or, stated another way, the third membrane 460 is not a leaky reverse osmosis membrane. The third membrane 460 comprises a polyamide, sulfonamide, nylon, or copolymer thereof.

The second permeate 456 is supplied to the third membrane cell 465. The third membrane 460 effectively and efficiently excludes most ions and metal complexes having an oxidation state of two or higher from passing through the pores of the third membrane 460, while allowing the hydrochloric to pass through to form a third permeate 466. Or, in other words, the third membrane 460 fractionates the uranium and nickel complexes from the hydrochloric acid in the second permeate 456, concentrating the uranium and nickel in a third retentate 468. The third retentate 468 has an uranium concentration commonly ranging from about 0.001 to about 0.2 g/L
(or, commonly from about 2x10"6 to about 5x10"4 moles of U/L) and more commonly of about 0.02 g/L, or about 10 times the concentrated of uranium in the second permeate 456, and a nickel concentration commonly ranging from about 1 to about 10 g/L (or, from about 6x10"3 to about 8x10-2 moles Ni/L) and more commonly of about 7 g/L, or about 10 times the concentration in the second permeate 456. Compared to the initial pregnant leach solution 430, the third permeate nickel concentration increased by a factor of about 14, from about 0.5 to about 7 grams of nickel per liter. The third retentate 468 is produced at rate of about 5 cubic meters per hour. The third retentate and permeate 466 comprise hydrochloride acid. The pH of the third retentate is preferably no more than about pH 1.5 while the pH of the third permeate preferably ranges from about pH 3 to about pH 3. The hydrochloric acid is sufficient for re-use as lixiviant 410. The permeate 466 is produced at a rate ranging from about 1 to about 40 cubic meters per hour.

The uranium in the first 448 and second 458 retentate solutions is recovered using conventional hydrometallurgical processes. It can be appreciated that, the first 448 and second 458 retentate solutions can be combined or processed separately.
The nickel in the third retentate solution 468 is recovered using conventional hydrometallurgical processes, such as precipitation and electrowinning.
This process configuration shows how target and other metal complexes may be separated from one another and isolated in retentate streams. Most of the target metal complexes are concentrated in the first and second retentates 448 and 458 while most of the other metal complexes are concentrated in the third retentate 468. To maintain a relatively high ratio of target metal complexes to other metal complexes in the first and second retentates, the first and second retentates typically contains from about 5 to less than about 50 vol.%
of the pregnant leach solution 430. Due to the effectiveness of the separation in the first and second membrane cells 445 and 455, the second permeate 456 contains no more than about 0.01 %
of the target metal complex in the pregnant leach solution 430. Most of this remaining target metal complex is removed in the third retentate along with most of the remaining other metal complex. At the low levels of concentration the other metal complex in the first and second retentates 448 and 458 and the target metal complex in the third retentate 468, target metal and other metal produces, respectively, of a sufficiently high purity can be recovered without significant economic contaminant penalties.

Fig. 5 depicts another process configuration for recovering a uranium sulfate complex by separating the target metal complex from one or more of other metal complex(es) and sulfuric acid. The other metal complex(es) is/are one or more metals typically associated in mineral deposits with uranium, such as, but not limited to, copper, cobalt, molybdenum, magnesium, vanadium, iron, silver, bismuth, lead, titanium, calcium, potassium, phosphorus, and fluorine.
The process configuration described below is not intended to be exhaustive or to limit the invention to the precise form disclosed in the following detailed description.
Rather, the process configuration was chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
Feed tank 501 contains a feed tank solution comprising the uranium sulfate complex, sulfuric acid, the other metal complex(es), and optionally an organic material. The organic material can be one or more of an oil, or other liquid organic material, and a solid material. The oil within feed tank solution can accumulate on top of the feed tank solution, due to its low specific gravity. In optional step 503, the accumulated oil layer can be removed by techniques well known to those skilled within the art, such as skimming or tapping oil layer. The organic material can come from a variety of sources but generally comes from upstream processing steps, particularly solvent extraction.

The feed tank solution is removed from the feed tank 501 by drawing, with a piping or tubing system, from the middle of the tank 501. Any particulate matter suspended within the feed tank solution can be removed by an optional micron filtration step 505.
Preferably, the micron filtration step is a one micro filter or less.

In optional step 507, any suspended, or emulsified oil and/or organic liquid, can be removed by a MYCELXTM filter, a viscoelastic absorbent filter media.
A positive displacement pump 509 supplies the feed tank solution comprising commonly from about 100 to about 300 g/L and more commonly about 110 g/L of uranyl sulfate and commonly from about 10 to about 300 g/L and more commonly about 160 g/L
sulfuric at a rate of commonly ranging from about 1 to about 20 and more commonly about 18 cubic meters per hour and pressure commonly ranging from about 40 to about 80 bar and more commonly of about 70 bar to header system 514.

The feed solution is treated by first, second, third, and fourth membrane banks 510, 520, 530, and 540. In one embodiment, the various membranes 516, 526, 536, and 546 in the banks are acid-resistant, loose or tight nanofiltration membranes, with an acid-resistant loose nanofiltration membrane being preferred. The membranes in the various filtration banks can have the same or differing pore size distributions depending on the configuration.
The header system 514 supplies the first membrane bank 510 with the feed tank solution.
The first membrane bank 510 is comprised of a first plurality of first membrane cells, preferably four first membrane cells. The first plurality of membrane cells forms a plurality of first retenates and permeates. The plurality of first retentates is collected by header system 515. And, the plurality of first permeates is collected by header system 550. The first retentates have a greater concentration of uranium sulfate than feed tank solution, and the first permeate a lesser concentration of uranium sulfate than the feed tank solution.
The header system 515 supplies the second membrane bank 520 with the first plurality of retentates. The second membrane bank 520 is comprised of a second plurality of second membrane cells, preferably three second membrane cells. The second plurality of membrane cells forms a plurality of second retentates and permeates. The plurality of second retentates is collected by header system 525. And, the plurality of second permeates is collected by header system 550. The second retentates have a greater concentration of uranium sulfate than the first plurality or retentates, and the second permeate a lesser concentration of uranium sulfate than the first plurality of retentates.

The header system 525 supplies the third membrane bank 530 with the second plurality of retentates. The third membrane bank 530 is comprised of a third plurality of third membrane cells, preferably two third membrane cells. The third plurality of membrane cells forms a plurality of third retentates and permeates. The plurality of third retentates is collected by header system 535. And, the plurality of third permeates is collected by header system 550. The third retentates having a greater concentration of uranium sulfate than the second plurality of retentates and the third permeate having a lesser concentration of uranium sulfate than the second plurality of retentates.

The header system 535 supplies the fourth membrane bank 540 with the third plurality of retentates. The fourth membrane bank 540 is comprised of a fourth plurality of fourth membrane cells, preferably two fourth membrane cells. The fourth plurality of membrane cells forms a plurality of fourth retentates and permeates. The plurality of fourth permeates is collected by header system 550. The fourth retentates have a greater concentration of uranium sulfate than the third plurality of retentates, and the fourth permeate has a lesser concentration of uranium sulfate than the third plurality of retentates.

The plurality of fourth retentates comprises at least most, and more preferably at least about 80%, of the uranium sulfate in the feed solution while the first, second, third, and fourth permeates comprise at least most, and preferably at least about 98%, of the sulfuric acid. In one implementation, the fourth retentate includes about 219 grams of uranium sulfate per liter and about 160 grams sulfuric acid per liter and is collected by header system 545 at a rate of about 9 cubic meters per hour. The plurality of retentates is processed to recover the uranium by methods know to those skilled within the art.
In one embodiment, the fourth membrane 546 is a tight or reverse osmosis membrane.
Preferably, the average pore size of the third membrane 546 is about equal to or less than the average pores size of the second membrane 536. More preferably, the fourth membrane is a reverse osmosis membrane that passes water and monovalent acids, particularly hydrochloric acid, while rejecting most larger monovalent acids and most higher valency compounds and complexes, such as di-, tri-, and higher valency metal complexes.
The header system 550 collecting the first, second, third and fourth permeates to form permeate solution 561, which can contains sufficiently clean sulfuric acid to be re-used as a lixiviant for leaching uranium. Or, permeate solution 561 can be optionally recycled in the process, re-entering the process at micron filter 505. In one implementation, the permeate solution 561 comprises about 9 grams uranium sulfate per liter and 160 grams sulfuric acid per liter is produced at a rate of about 9 cubic meters per hour.

In another implementation, the feed tank solution comprises about 110 grams of uranium sulfate per liter and about 30 wt% of sulfuric acid and is supplied to optional micron filer 505 at a rate of 100 liters per minute. After optional micron filter 505, the feed solution is processed as described above, the plurality of fourth permeates comprising about 10 grams of uranium sulfate per liter and about 30 wt% sulfuric acid is produced at a rate of about 50 liters per minute. The fourth plurality of retentates comprising about 230 grams uranium sulfate per liter and about 30 wt% sulfuric acid is produced at rate of about 50 liters per minute. The fourth plurality of retentates and permeates are processed as described above.

EXPERIMENTAL
Example A

A pregnant solution having 300 grams/liter sulfuric acid and about 115 gram/l uranium is supplied at a temperature of about 40 C and a pressure of about 900 psi to a membrane cell having an acid-stable loose nanofiltration membrane having an average pore size of about 15 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 13 to about 17 Angstroms. The membrane rejected about 53% of the uranium.
Example B

A pregnant solution having 300 grams/liter sulfuric acid and about 115 gram/l uranium is supplied at a temperature of about 40 C and a pressure of about 900 psi to membrane cell having an acid stable tight nanofiltration membrane having an average pore size of about 10 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms. The membrane rejected about 95% of the uranium.
Example C

A pregnant solution having 114 grams of uranium per liter and 275 gram of acid is supplied at a pressure of about 500 psi to a first membrane cell having an acid stable loose nanofiltration membrane having an average pore size of about 15 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 13 to about 17 Angstroms. Twenty liters of the pregnant solution is processed by the first membrane cell, producing 5 liters of a first retentate having 188 grams of uranium per liter and 272 grams acid per liter and 15 liters of a first permeate having 89 grams uranium per liter and 266 grams of acid per liter. The first permeate is supplied at a pressure of about 850 psi to a second membrane cell having an acid stable tight nanofiltration membrane having an average pore size is about 10 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms. The second membrane cell produces 5 liters of a second retentate having 234 grams of uranium per liter and 276 grams of acid per liter and 10 liters of a second permeate having 9.5 grams uranium per liter and 281 grams of acid per liter. The uranium was extracted from the combined first and second retentates. The acid was stripped from the second permeate for reuse as a lixiviant.
Example D

A pregnant solution having 113 grams of uranium per liter and 260 grams per liter of acid is supplied at a pressure of about 900 psi to a membrane cell having an acid stable tight nanofiltration membrane having an average pore size of about 10 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms. After processing 101iters of pregnant solution, the membrane cell produces 5 liter of retentate having 236 grams of uranium per liter and 278 grams of acid per liter and 5 liters of permeate having 11 grams of uranium per liter and 280 grams of acid per liter.
The acid was stripped from the permeate for reuse as a lixiviant.
Example E

A pregnant solution having 0.2 grams/liter uranium and 0.93 gram/1 molybdenum was supplied at a pressure of about 850 psi to membrane cell having a tight nanofiltration membrane comprised of a first acid stable polymer composition. The membrane having an average pore size of about 10 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms. The membrane cell a 66% recovery rate, producing a retentate having an uranium concentration of 0.52 g/1 and a molybdenum concentration of 1.76 g/1, and a permeate having an uranium concentration of 0.011 g/1 and a molybdenum concentration of 0.05 g/1.
Example F

A pregnant solution having 0.2 grams/liter uranium and 0.93 gram/1 molybdenum was supplied at a pressure of about 500 psi to membrane cell having a tight nanofiltration membrane comprised of a second acid stable polymer composition. The membrane having an average pore size of about 10 Angstroms and a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms. The membrane cell a 75%
recovery rate, producing a retentate having an uranium concentration of 0.77 g/l and a molybdenum concentration of 2.25 g/1, and a permeate having an uranium concentration of 0.02 g/l and a molybdenum concentration of 0.33 g/1.
Example G

The rejection rate of various membranes were determined when processing 30%
sulfuric acid and 11% uranium at a temperature of 25 C and a driving pressure of 200 psi.

Membrane Type % Rejection % Rejection Flux-GFD Flux GFD Flux GFD
Standard Conditions P. S. S. At Standard Acid + U Post Acid + U

Loose NF-G 56% 39% 16.8 13.6 15.9 Loose NF-K 67% 55% 30.6 17.25 27.7 Tight NF-D 75.5% 95% 19.8 4.9 17.6 Tight NF-K 78% 95% 18.25 4.7 17.6 Tight NF-A 81% 80.40% 28.7 4.2 19.7 GFD-is Gallons per Ft.2 per Day of active area A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others.
For example, hyperfiltration membranes may be used instead of nanofiltration membranes.

The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure.
The present invention, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and\or reducing cost of implementation.
The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention.

Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.

Claims

What is claimed is:

1. A method for recovering a target metal complex from one or more non-target metal complexes, comprising:

providing a pregnant solution comprising a target metal complex, lixiviant, and non-target metal complex, wherein the target metal has an oxidation state of at least about four while the non-target metal has an oxidation state of no more than about 3;
providing at least one semi-permeable membrane capable of rejecting at least most of the target metal complex while passing at least most of the non-target metal complex and/or at least most of the lixiviant;

contacting the pregnant solution with the at least one semi-permeable membrane to produce a retentate and permeate, wherein the retentate comprises at least most of the target metal complex in the pregnant solution and the permeate comprises at least most of the non-target metal complex and/or lixiviant.

2. The method of claim 1, wherein the lixiviant is an acid selected from the group consisting essentially of hydrochloric acid, nitric acid, sulfuric acid, citric acid, acetic acid, and a mixtures thereof, wherein the target metal is selected from the group consisting essentially of a lanthanide series metal, an actinide series metal, and mixtures thereof, and wherein the non-target metal is selected from the group consisting essentially of an s-block metal, an alkaline earth metal, a d-block transition metal, an inner transition f-block metal other than uranium, and mixtures thereof.

3. The method of claim 1, wherein one or more of the following is true for the at least one semi-permeable membrane:

(i) the at least one semi-permeable membrane has an average pore size ranging from about 8 to about 12 Angstroms;

(ii) the at least one semi-permeable membranes has an average pore size ranging from about 13 to about 17 Angstroms;

(iii) the least one semi-permeable membrane has a pore size distribution wherein at least about 80% of the pores range in size from about 8 to about 12 Angstroms; and (iv) the at least one semi-permeable membrane has a pore size distribution wherein at least about 80% of the pores range in size from about 13 to about 17 Angstroms.

4. The method of claim 3, wherein the at least one semi-permeable membrane is substantially stable at a pH value of about 2 or less, a filtration pressure ranging from about 100 to about 1,500 psi, an acid concentration ranging from about 0.1 to about 30 wt% acid, and a temperature ranging from about 5 to about 95 °C, and wherein the at least one semi-permeable membrane has a thickness ranging from about 1,000 to about 3,000 Angstroms.

5. The method of claim 1, wherein the at least one semi-permeable membrane comprises a polyamide, nylon, sulfonamide, or copolymer thereof.

6. The method of claim 1, wherein the at least one semi-permeable membrane comprises a plurality of membranes, wherein a first set of the membranes is connected in parallel, wherein a second set of the membranes is connected in parallel, wherein the first set of membranes is connected in series with the second set of membranes, wherein each membrane in the first set is a loose nanofiltration membrane, and wherein each membrane in the second set is a tight nanofiltration membrane.

7. The method of claim 6, wherein at least part of the retentate of the second set is combined with the pregnant solution and inputted into the first set.

8. The method of claim 1, wherein the permeate comprises at least most of the non-target metal complex and further comprising:
passing the permeate through a second semi-permeable membrane to form a second permeate and retentate, wherein the second retentate comprises at least most of the non-target metal complex in the permeate.

9. The method of claim 8, wherein the second semi-permeable membrane is a reverse osmosis membrane and wherein the second retentate comprises at least most of the lixiviant in the permeate.

10. The method of claim 3, wherein at least one of the following is true:
(a) both (i) and (iii) are true; and (b) both (ii) and (iv) are true.

11. The retentate formed by the method of claim 1.

12. A method for recovering uranium from a pregnant solution, comprising:
providing a pregnant solution comprising a uranium complex and a lixiviant, the pregnant solution having a pH of no more than about pH 5;

contacting the pregnant solution with the one or more acid-resistant nanofiltration membranes to produce a retentate comprising at least most of the uranium complex in the pregnant solution and a permeate comprising at least most of the lixiviant in the pregnant solution.

13. The method of claim 12, wherein the lixiviant is an acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, citric acid, acetic acid, and a mixture thereof and wherein the one or more nanofiltration membranes comprises a polyamide, nylon, sulfonamide, or copolymer thereof.

14. The method of claim 12, wherein one or more of the following is true:
(i) at least one filtration membrane of the one or more filtration membranes has an average pore size ranges from about 8 to about 12 Angstroms;
(ii) at least one filtration membrane of the one or more filtration membranes has an average pore size ranges from about 13 to about 17 Angstroms;
(iii) at least one filtration membrane of the one or more filtration membranes has a pore size distribution where at least about 80% of the pores range in size from about 8 to about 12 Angstroms; and (iv) at least one filtration membrane of the one or more filtration membranes has a pore size distribution where at least about 80% of the pores range in size from about 13 to about 17 Angstroms.

15. The method of claim 12, wherein the pregnant solution comprises a metal complex, wherein the metal in the metal complex has an oxidation number of three or less, wherein the permeate comprises most of the metal complex in the pregnant solution, wherein the filtration membrane is substantially stable when operating at a pH value of about 2 or less, a filtration pressure ranging from about 100 to about 1,500 psi, and an acid concentration ranging from about 0.1 to about 30 wt% acid.

16. The method of claim 12, wherein the filtration membrane comprises a polyamide, nylon, sulfonamide, or copolymer thereof.

17. The method of claim 15, further comprising:
passing the permeate through a reverse osmosis membrane to produce a second permeate and a second retentate, wherein the second retentate comprises at least most of the metal complex in the pregnant solution.

18. A method, comprising:
Contacting an acid with a uranium ore to form a pregnant leach solution comprising the acid and a uranyl complex;

contacting the pregnant leach solution with a nanofiltration membrane to form a permeate and a retentate, wherein the nanofiltration passes the acid but rejects the uranyl complex.

19. The method of claim 18, wherein the ore comprises nickel, wherein the acid dissolved the nickel as a nickel complex into the pregnant leach solution, and wherein the nanofiltration passes the nickel complex to effect separation of the uranyl complex from the nickel complex.