U.S. patent application number 13/454226 was filed with the patent office on 2012-10-04 for process for recovering metals and metal compounds from mined ore and other metal-bearing raw source materials.
Invention is credited to Peter T. HALPIN, Ulrich R. SCHLEGEL, Dale L. SCHNECK.
Application Number | 20120247271 13/454226 |
Document ID | / |
Family ID | 43030484 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120247271 |
Kind Code |
A1 |
HALPIN; Peter T. ; et
al. |
October 4, 2012 |
PROCESS FOR RECOVERING METALS AND METAL COMPOUNDS FROM MINED ORE
AND OTHER METAL-BEARING RAW SOURCE MATERIALS
Abstract
A filter cake, including a first metal in an insoluble form
and/or filtrate comprising Cr in a soluble form, obtained by a
method involving filtering an aqueous slurry of a metal-bearing raw
source material comprising the first metal in an insoluble form,
soluble and/or insoluble Cr in a Cr bearing material as a second
metal, and organic and inorganic compounds, after adjusting the pH
of the slurry to an alkaline pH sufficient to convert soluble Cr
present to an insoluble form and selectively leaching the Cr by
adding a leaching agent in an amount sufficient to convert Cr to a
soluble form while the first metal remains in the slurry in an
insoluble form.
Inventors: |
HALPIN; Peter T.; (Great
Falls, VA) ; SCHLEGEL; Ulrich R.; (Washington,
DC) ; SCHNECK; Dale L.; (Pottsville, PA) |
Family ID: |
43030484 |
Appl. No.: |
13/454226 |
Filed: |
April 24, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12770134 |
Apr 29, 2010 |
8177882 |
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13454226 |
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61174205 |
Apr 30, 2009 |
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61293419 |
Jan 8, 2010 |
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Current U.S.
Class: |
75/300 ; 420/428;
75/739 |
Current CPC
Class: |
C22B 7/008 20130101;
C22B 23/0453 20130101; C22C 19/07 20130101; C01G 45/02 20130101;
C22C 19/03 20130101; Y02P 10/234 20151101; C22B 7/006 20130101;
C01G 37/02 20130101; C22B 34/32 20130101; Y02P 10/20 20151101; C22B
3/44 20130101 |
Class at
Publication: |
75/300 ; 75/739;
420/428 |
International
Class: |
C22B 3/12 20060101
C22B003/12; C22C 27/06 20060101 C22C027/06; C22B 34/32 20060101
C22B034/32 |
Claims
1. A filter cake produced by a method for selectively recovering a
metal from a metal-bearing raw source material, the method
comprising: a) mixing with an aqueous medium a metal-bearing raw
source material comprising a first metal in an insoluble form,
soluble and/or insoluble Cr in a Cr bearing material as a second
metal, and organic and inorganic compounds to obtain a slurry
comprising the first metal in an insoluble form, soluble and/or
insoluble Cr in a Cr bearing material and the organic and inorganic
compounds; b) adjusting the pH of the slurry to an alkaline pH
sufficient to convert soluble Cr present to an insoluble form; c)
optionally adding a first oxidizer to the slurry to facilitate
subsequent oxidation steps; d) selectively leaching the Cr by
adding a leaching agent in an amount sufficient to convert Cr to a
soluble form while the first metal remains in the slurry in an
insoluble form; e) filtering the slurry to obtain a filter cake
comprising the first metal in an insoluble form and a filtrate
comprising Cr in a soluble form; f) recovering the filter cake
comprising the first metal in an insoluble form and/or filtrate
comprising Cr in a soluble form; and comprising said first
metal.
2. A filtrate produced by the method for selectively recovering a
metal from a metal-bearing raw source material, the method
comprising: a) mixing with an aqueous medium a metal-bearing raw
source material comprising a first metal in an insoluble form,
soluble and/or insoluble Cr in a Cr bearing material as a second
metal, and organic and inorganic compounds to obtain a slurry
comprising the first metal in an insoluble form, soluble and/or
insoluble Cr in a Cr bearing material and the organic and inorganic
compounds; b) adjusting the pH of the slurry to an alkaline pH
sufficient to convert soluble Cr present to an insoluble form; c)
optionally adding a first oxidizer to the slurry to facilitate
subsequent oxidation steps; d) selectively leaching the Cr by
adding a leaching agent in an amount sufficient to convert Cr to a
soluble form while the first metal remains in the slurry in an
insoluble form; e) filtering the slurry to obtain a filter cake
comprising the first metal in an insoluble form and a filtrate
comprising Cr in a soluble form; f) recovering the filter cake
comprising the first metal in an insoluble form and/or filtrate
comprising Cr in a soluble form; and comprising Cr in a soluble
form.
3. The method for selectively recovering nickel (Ni) and chromium
(Cr) from a metal-bearing raw source material, comprising: a)
mixing with an aqueous medium a metal-bearing raw source material
comprising Ni compound(s) in an insoluble form as a first metal,
insoluble and/or soluble Cr compound(s) as a second metal, and
organic and inorganic compounds to obtain a slurry comprising Ni in
an insoluble form, insoluble and/or soluble Cr, and the organic and
inorganic compounds; b) adjusting the pH of the slurry to
facilitate subsequent oxidation steps; c) adding a first oxidizer
to the slurry to oxidize the organic and inorganic compounds, d)
adding MnO.sub.4.sup.- to the slurry in an amount sufficient to
oxidize the Cr into a soluble form while the Ni remains in the
slurry in an insoluble form; e) filtering the slurry to obtain a
filter cake comprising Ni in an insoluble form and a filtrate
comprising Cr in a soluble form; f) recovering the filter cake
comprising Ni in an insoluble form; g) optionally recovering the
filtrate comprising Cr in a soluble form; wherein step g) further
comprises: (I) treating the filtrate comprising Cr in a soluble
form with an acid to obtain an acidic solution; (II) adding a
reducing agent to the acidic solution while mixing to reduce the Cr
in a soluble form to an insoluble form; (III) adjusting the pH of
the acidic solution to a basic solution to form a solution
comprising Cr hydroxide precipitate (Cr(OH).sub.3); and (IV)
filtering the solution comprising Cr(OH).sub.3 precipitate to
obtain a filter cake comprising Cr(OH).sub.3 and a basic
solution.
4. The method according to claim 3, further comprising (V)
reslurrying the Cr(OH).sub.3 filter cake to wash out sulfates and
other water soluble compounds, and (VI) filtering the slurry
comprising washed Cr(OH).sub.3 filter cake to obtain a second
Cr(OH).sub.3 filter cake.
5. The method according to claim 3, further comprising adding a
sufficient amount of reducing agent to step (II) to obtain a
reaction as follows:
2CrO.sub.4.sup.-2+2Na.sub.2S.sub.2O.sub.5=2Cr.sup.+3+4NaSO.sub.-
4+O.sub.2. (3)
6. The method according to claim 5, wherein a sufficient amount of
base is added to obtain a reaction as follows:
Cr.sup.+3+3NaOH=Cr(OH).sub.3+3Na.sup.+ (4) wherein Cr(OH).sub.3 is
a precipitate.
7. The method for selectively recovering nickel (Ni) and chromium
(Cr) from a metal-bearing raw source material, comprising: a)
mixing with an aqueous medium a metal-bearing raw source material
comprising Ni compound(s) in an insoluble form as a first metal,
insoluble and/or soluble Cr compound(s) as a second metal, and
organic and inorganic compounds to obtain a slurry comprising Ni in
an insoluble form, insoluble and/or soluble Cr, and the organic and
inorganic compounds; b) adjusting the pH of the slurry to
facilitate subsequent oxidation steps; c) adding a first oxidizer
to the slurry to oxidize the organic and inorganic compounds, d)
adding MnO.sub.4.sup.- to the slurry in an amount sufficient to
oxidize the Cr into a soluble form while the Ni remains in the
slurry in an insoluble form; e) filtering the slurry to obtain a
filter cake comprising Ni in an insoluble form and a filtrate
comprising Cr in a soluble form; f) recovering the filter cake
comprising Ni in an insoluble form; g) optionally recovering the
filtrate comprising Cr in a soluble form; wherein step g) further
comprises: passing the filtrate comprising Cr in a soluble form
over an ion exchange column, wherein the ion exchange column binds
Cr and provides a cleaned aqueous fraction, eluting the ion
exchange column with a buffer to obtain a fraction comprising Cr in
a soluble form, and optionally concentrating the fraction
comprising Cr in a soluble form.
8. A Cr(VI) product produced by the method according to claim
7.
9. A filter cake produced by the process according to claim 6,
wherein the filter cake comprises Cr(OH).sub.3.
10. A method for selectively recovering nickel (Ni) and chromium
(Cr) from a metal-bearing raw source material, comprising: a)
mixing with an aqueous medium a metal-bearing raw source material
comprising Ni compound(s) in insoluble form, insoluble and/or
soluble Cr compound(s) and organic and inorganic compounds to
obtain a slurry comprising the first metal in an insoluble form,
insoluble Cr, and the organic and inorganic compounds; b) adding a
hydroxide to the slurry to raise the pH of the slurry to 12.0-12.5
and in an amount sufficient to form chromium hydroxide
(Cr(OH).sub.3), chromium oxide (Cr.sub.2O.sub.3), or mixtures
thereof; c) adding a first oxidizer comprising calcium hypochlorite
to the slurry in an amount sufficient to oxidize said organic and
inorganic compounds; d) adding a second oxidizer comprising
MnO.sub.4.sup.- to the slurry in an amount sufficient to react with
the Cr(OH).sub.3, Cr.sub.2O.sub.3, or mixtures thereof as follows:
2Cr(OH).sub.3+4MnO.sub.4.sup.-=2CrO.sub.4.sup.-2+MnO.sub.2+3O.sub.2
or (1)
2Cr.sub.2O.sub.3+4MnO.sub.4.sup.-=4CrO.sub.4.sup.-2+8MnO.sub.2+3O.su-
b.2, (2) wherein CrO.sub.4.sup.-2 is soluble and remains in the
slurry to provide a chromate solution and MnO.sub.2 is an oxide
precipitate; e) filtering the slurry to obtain a filter cake
comprising Ni in an insoluble form and filtrate comprising
chromate; f) recovering the filter cake comprising Ni; g) treating
the filtrate comprising Cr(VI) with acid in an amount sufficient to
obtain an acidic solution comprising Cr(VI); h) adding sodium
metabisulfite to the acidic solution in an amount sufficient so
that the Cr(VI) reacts with the sodium metabisulfite to obtain a
reaction as follows:
2CrO.sub.4.sup.-2+2Na.sub.2S.sub.2O.sub.5=2Cr.sup.+3+4NaSO.sub.4+O.sub.2
(3) i) adjusting pH of the acidic solution with a hydroxide in an
amount sufficient to obtain a reaction as follows:
Cr.sup.+3+3NaOH=Cr(OH).sub.3+3Na.sup.+ (4) wherein Cr(OH).sub.3 is
a Cr hydroxide precipitate; j) filtering the solution comprising
Cr(OH).sub.3 to obtain a Cr(OH).sub.3 filter cake; and k)
recovering the Cr filter cake.
11. A filter cake obtained by the process according to claim 10,
wherein the filter cake comprises Ni.
12. A filter cake obtained by the process according to claim 10,
wherein the filter cake comprises Cr(OH).sub.3.
13. A method for selectively recovering nickel (Ni) and chromium
(Cr) from a metal-bearing raw source material, comprising: a)
mixing with an aqueous medium a metal-bearing raw source material
comprising Ni in insoluble form, soluble and/or insoluble Cr in a
Cr bearing material and organic and inorganic compounds to obtain a
slurry comprising the first metal in an insoluble form, soluble
and/or insoluble Cr, and the organic and inorganic compounds; b)
adding a hydroxide to the slurry to raise the pH of the slurry to
12.0-12.5 and in an amount sufficient to form chromium hydroxide
(Cr(OH).sub.3) chromium oxide (Cr.sub.2O.sub.3), or mixtures
thereof; c) adding a first oxidizer comprising calcium hypochlorite
to the slurry in an amount sufficient to oxidize said organic and
inorganic compounds; d) adding a second oxidizer comprising
MnO.sub.4.sup.- to the slurry in an amount sufficient to react with
the Cr(OH).sub.3, Cr.sub.2O.sub.3, or mixtures thereof as follows:
2Cr(OH).sub.3+4MnO.sub.4.sup.-=2CrO.sub.4.sup.-2+MnO.sub.2+3O.sub.2
or (1)
2Cr.sub.2O.sub.3+4MnO.sub.4.sup.-=4CrO.sub.4.sup.-2+8MnO.sub.2+3O.su-
b.2, (2) wherein CrO.sub.4.sup.-2 is soluble and remains in the
slurry to provide a Cr(VI) solution and MnO.sub.2 is an oxide
precipitate; e) filtering the slurry to obtain a filter cake
comprising Ni in an insoluble form and a filtrate comprising
Cr(VI); f) recovering the filter cake comprising Ni in an insoluble
form; g) passing the filtrate comprising Cr(VI) over an ion
exchange column, wherein the ion exchange column binds Cr(VI) and
provides a cleaned aqueous fraction; h) eluting the ion exchange
column with a buffer to obtain a concentrated Cr(VI) fraction
having Cr in an amount 5-10 fold more than present in the filtered
Cr(VI) solution; and i) recovering a concentrated Cr(VI)
fraction.
14. A filter cake obtained by the process according to claim 13,
wherein the filter cake comprises Ni.
15. A Cr(VI) fraction produced by the process according to claim
13, wherein the filter cake comprises Cr.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 12/770,134 filed Apr. 29, 2010 which claims the benefit under
35 USC 119(e) of provisional application No. 61/174,205 filed Apr.
30, 2009 and No. 61/293,419 filed Jan. 8, 2010, all of which are
fully incorporated herein by reference.
BACKGROUND
[0002] A. Field
[0003] The present invention relates to a method for selectively
recovering a metal, groups of metals, and/or metal compound(s) from
a metal-bearing raw source material containing chromium (Cr).
[0004] B. Related Art
[0005] Industrial, mining, and manufacturing processes generate
large amounts of metal-bearing raw source material on daily basis.
This metal-bearing raw source material includes mining ores, ore
concentrates, waste products, residues and byproducts.
Metal-bearing raw source material often contains valuable
nonferrous metals such as chromium (Cr), nickel (Ni), copper (Cu),
cobalt (Co), tin (Sn), zinc (Zn), molybdenum (Mo), manganese (Mn),
lead (Pb), cadmium (Cd), vanadium (V), as well as precious and
platinum group metals including silver (Ag), gold (Au), palladium
(Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium (Os), and
iridium (Ir).
[0006] The disposal of metal-bearing raw source material containing
these metals raises serious environmental and business concerns on
a global level due to the hazardous nature, potential toxicity, and
risk to human health posed by the presence of these metals. The
costs associated with the disposal of hazardous metal-bearing raw
source material in the absence of metal reclamation are enormous.
In this regard, recovery of metals from metal-bearing raw source
material not only would reduce the volume and cost of disposal, but
the recovered metals could be resold or reused to provide
substantial economic value. The expenses and environmental impact
associated with disposing of metal-bearing raw source material,
along with the economic value of the incorporated metals, has
generated interest in how to treat and recover metals from
metal-bearing raw source material.
[0007] Current methods for treating and recovering metals from
metal-bearing raw source material, however, are often inefficient
and expensive to implement. It has been particularly challenging to
treat and recover metals from metal-bearing raw source material
that contains Cr, as Cr is difficult to separate from other metals
and metal compounds.
[0008] For example, vitrification is a proven technique in the
disposal and long-term storage of nuclear waste. However, the
presence of Cr dramatically increases the bulk of the nuclear
waste. In order to economize and reduce the quantity of nuclear
waste, the Cr content is hydrometallurgically separated and
removed, thereby decreasing the total amount of nuclear waste to be
vitrified. See Rapko et al., "Selective Leaching of Chromium from
Hanford Tank Sludge 241-U-108", Pacific Northwest National
Laboratory, PNNL-14019, article prepared for the U.S. Department of
Energy under Contract DE-AC06-76L01830. Rapko et al disclose that
the Cr can be selectively leached from the nuclear waste through an
oxidative alkaline leaching process. The process, however, utilizes
expensive reactants and is not concerned with the recovery or
economic value of other metals that might be present in the nuclear
waste. The primary objective of Rapko et al. is to effectively
reduce the vitrification cost by reducing the quantity of nuclear
waste to be vitrified. The removal of the Cr component from the
nuclear waste satisfies this objective by reducing the final
quantity of waste that must be vitrified, thus lowering the overall
cost of processing.
[0009] U.S. Pat. No. 5,200,088 describes a process for removing
hexavalent chromium (Cr(VI)) from a waste product. This patent
suggests that the most hazardous form of chromium is Cr(VI) and
that the presence of Cr(VI) in the waste product must be reduced to
a few parts per million (ppm) or less before the waste product can
be discarded. In accordance with the process described in this
patent, the Cr(VI) in the waste product is converted by treating
the waste product with an alkali metal dithionite to reduce the
Cr(VI) to trivalent chromium (Cr (III)). The result is a soluble
material that forms a precipitate at reduced pH. The precipitate
containing the Cr(III) can then be separated from the remaining
waste product. However, the patent does not reveal any interest in
the recovery or separation of other metals that may be present in
the Cr-bearing waste.
[0010] U.S. Pat. No. 4,162,294 describes a method for recovering Cr
and at least one other metal from a metal-bearing raw source
material containing Cr. In particular, the method involves
chlorinating a waste sludge containing Cr, aluminum (Al), Cu, Zn,
and Ni to oxidize the Cr into a soluble form and to obtain an
insoluble component that contains the Al, Cu, Zn, and Ni;
separating the Cr in soluble form from the insoluble component with
a fixed bed anion exchanger; and separating the Al, Cu, Zn, and Ni
present in the insoluble component through an elaborate series of
liquid-liquid extractions and precipitation steps.
[0011] However, ion exchange is relatively costly, slow, and
cumbersome to use. In order to be effective, the Cr-bearing
material being treated must be passed through a significant amount
of ion-exchange resin, usually in the form of a filter bed, making
it effective, in most cases, for treating only small volumes of
wastewater. Thus, ion exchange would be impractical as an initial
step for separating metals from complex metal-bearing raw source
material. Furthermore, the series of liquid-liquid extractions and
precipitation steps is also inefficient. When the ion exchange step
and series of liquid-liquid extractions and precipitation are used
in combination, the method is particularly inefficient and
expensive to execute.
[0012] While the above publications focus on the removal of Cr, or
the recovery of Cr and other metals with complicated and expensive
processes, none of them are seen to disclose a method capable of
selectively recovering at least one metal from a metal-bearing raw
source material containing Cr in an efficient, relatively low cost
manner.
SUMMARY
[0013] The present invention is based on the discovery of an
efficient and effective method for selectively recovering at least
one metal from a metal-bearing raw source material containing Cr in
a soluble or insoluble form.
[0014] In a preferred embodiment of the invention, Ni is also
recovered from a metal-bearing raw source material containing Ni
and Cr.
[0015] More specifically, in accordance with a first aspect of the
invention, a method for selectively recovering a metal from a
metal-bearing raw source material comprises: [0016] a) mixing with
an aqueous medium a metal-bearing raw source material comprising a
first metal in an insoluble form, soluble and/or insoluble Cr in a
Cr bearing material as a second metal, and organic and inorganic
compounds to obtain a slurry comprising the first metal in an
insoluble form, soluble and/or insoluble Cr in a Cr bearing
material and the organic and inorganic compounds; [0017] b)
adjusting the pH of the slurry to an alkaline pH sufficient to
convert soluble Cr to an insoluble form; [0018] c) optionally
adding a first oxidizer to the slurry to facilitate subsequent
oxidation steps; [0019] d) selectively leaching the Cr by adding a
leaching agent in an amount sufficient to convert Cr to a soluble
form while the first metal remains in the slurry in an insoluble
form; [0020] e) filtering the slurry to obtain a filter cake
comprising the first metal in an insoluble form and a filtrate
comprising Cr in a soluble form; [0021] f) recovering the filter
cake comprising the first metal in an insoluble form and/or
filtrate comprising Cr in a soluble form.
[0022] In accordance with another aspect of the invention, the
first metal is Ni.
[0023] According to another aspect of the invention, Ni and Cr are
selectively recovered from a metal-bearing raw source material in a
process comprising: [0024] a) mixing with an aqueous medium a
metal-bearing raw source material comprising Ni compound(s) in an
insoluble form as a first metal, insoluble Cr compound(s) as a
second metal, and organic and inorganic compounds to obtain a
slurry comprising Ni in an insoluble form, insoluble Cr, and the
organic and inorganic compounds; [0025] b) adjusting the pH of the
slurry to facilitate subsequent oxidation steps; [0026] c)
optionally adding a first oxidizer to the slurry to oxidize the
organic and inorganic compounds, [0027] d) adding a second oxidizer
to the slurry in an amount sufficient to oxidize the Cr into a
soluble form while the Ni remains in the slurry in an insoluble
form; [0028] e) filtering the slurry to obtain a filter cake
comprising Ni in an insoluble form and a filtrate comprising Cr in
a soluble form; [0029] f) recovering the filter cake comprising Ni
in an insoluble form; and [0030] g) optionally recovering the
filtrate comprising Cr in a soluble form.
[0031] In accordance with another aspect of the invention, Ni and
Cr are recovered from Ni and Cr bearing materials by a method
comprising: [0032] a) mixing with an aqueous medium a metal-bearing
raw source material comprising Ni compound(s) in insoluble form,
insoluble Cr compound(s) and organic and inorganic compounds to
obtain a slurry comprising the first metal in an insoluble form,
insoluble Cr, and the organic and inorganic compounds; [0033] b)
adding a hydroxide to the slurry to raise the pH of the slurry to
12.0-12.5 and in an amount sufficient to form chromium hydroxide
(Cr(OH).sub.3), chromium oxide (Cr.sub.2O.sub.3), or mixtures
thereof; [0034] c) adding a first oxidizer comprising calcium
hypochlorite to the slurry in an amount sufficient to oxidize said
organic and inorganic compounds; [0035] d) adding a second oxidizer
comprising MnO.sub.4.sup.- to the slurry in an amount sufficient to
react with the Cr(OH).sub.3, Cr.sub.2O.sub.3, or mixtures thereof
as follows:
[0035]
2Cr(OH).sub.3+4MnO.sub.4.sup.-=2CrO.sub.4.sup.-2+MnO.sub.2+3O.sub-
.2 or (1)
2Cr.sub.2O.sub.3+4MnO.sub.4.sup.-=4CrO.sub.4.sup.-2+8MnO.sub.2+3O.sub.2,
(2)
[0036] wherein CrO.sub.4.sup.-2 is soluble and remains in the
slurry to provide a chromate solution and MnO.sub.2 is an oxide
precipitate; [0037] e) filtering the slurry to obtain a filter cake
comprising Ni in an insoluble form and filtrate comprising
chromate; [0038] f) recovering the filter cake comprising Ni;
[0039] g) treating the filtrate comprising Cr(VI) with acid in an
amount sufficient to obtain an acidic solution comprising Cr(VI);
[0040] h) adding sodium metabisulfite to the acidic solution in an
amount sufficient so that the Cr(VI) reacts with the sodium
metabisulfite to obtain a reaction as follows:
[0040]
2CrO.sub.4.sup.-2+2Na.sub.2S.sub.2O.sub.5=2Cr.sup.+3+4NaSO.sub.4+-
O.sub.2 (3) [0041] i) adjusting pH of the acidic solution with a
hydroxide in an amount sufficient to obtain a reaction as
follows:
[0041] Cr.sup.+3+3NaOH=Cr(OH).sub.3+3Na.sup.+ (4)
[0042] wherein Cr(OH).sub.3 is a Cr hydroxide precipitate; [0043]
j) filtering the solution comprising Cr(OH).sub.3 to obtain a
Cr(OH).sub.3 filter cake; and [0044] k) recovering the Cr filter
cake.
[0045] Additional details and variations of the described processes
embodying the invention will be described in the detailed
description below.
BRIEF DESCRIPTION OF THE DRAWING
[0046] FIG. 1 is a flowchart exemplifying a method for recovering
Ni and Cr from a Ni/Cr raw material in accordance with the
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0047] The phrase "selectively leach" as used herein means to wash,
extract, or perform a chemical reaction to separate a soluble
element or compound from an insoluble material.
[0048] The phrase "insoluble form" means an element in free form or
compound incapable of or that resists dissolving in a particular
solvent.
[0049] A "metal-bearing raw source material" is any material that
contains a metal. This includes waste, residue, ore, ore
concentrate, byproduct, processed, and/or unprocessed material.
[0050] The phrase "plating sludge" is a hydroxide sludge, which has
been formed during the treatment of waste liquor, metal plating, or
other metal finishing processes and waste waters which may or may
not be dehydrated.
[0051] A "Ni/Cr raw material" is a material that contains Ni and Cr
and/or Ni and Cr compounds and potentially other metals of
value.
[0052] The phrase "predetermined criteria" means a previously
determined standard that a metal-bearing raw source material must
meet regarding a specific economic and elemental threshold, before
being processed in accordance with the present invention.
[0053] The present invention relates to a method for selectively
recovering a metal from a metal-bearing raw source material. The
method involves mixing in an aqueous medium a metal-bearing raw
source material containing (i) a first metal in an insoluble form,
(ii) insoluble and/or soluble Cr in a Cr bearing material as a
second metal, and (iii) organic and inorganic compounds to obtain a
slurry. The slurry contains the first metal in an insoluble form to
be recovered, the Cr bearing material, and the organic and
inorganic compounds.
[0054] The first metal remains insoluble throughout the method. The
first metal is preferably in an insoluble form that is incapable of
or resists dissolving so that less than 1.0% of the first metal is
in a soluble form at any given time during the method.
[0055] The pH of the slurry is then adjusted to facilitate the
efficient oxidation of Cr in subsequent steps. The pH is preferably
adjusted to an alkaline state, and more preferably to a pH of 12.0
to 12.5 to convert soluble Cr to insoluble Cr.
[0056] A first oxidizer is optionally added to the slurry to
oxidize extraneous organic and inorganic compounds present in the
slurry. The Cr in an initially insoluble form can then be
selectively leached from insoluble components that may be present
in the slurry by adding a leaching agent in an amount sufficient to
obtain Cr in a soluble form. While the Cr will be converted to a
soluble form, the first metal remains in the slurry in an insoluble
form. The slurry may then be filtered to obtain a filter cake
containing the first metal in an insoluble form and a filtrate
containing Cr in a soluble form.
[0057] The filter cake containing the first metal in an insoluble
form and/or filtrate comprising Cr in a soluble form may then be
recovered.
[0058] The filter cake optionally contains additional metals (i.e.,
a third metal) that were present in the raw material and recovered
along with the first metal. The other base, precious, and platinum
group metals that may be recovered include but are not limited to
Ni, Cu, Co, Sn, Zn, Mo, Mn, Pb, Cd, V, Ag, Au, Pd, Pt, Rh, Ru, Os,
and Ir
[0059] In a preferred embodiment of this invention, the first metal
is Ni.
[0060] FIG. 1 depicts in a flowchart a preferred method for
recovering Ni and Cr from a Ni/Cr raw material. The selected Ni/Cr
raw material (110) may be any material that contains Ni and Cr,
such as metal bearing ores and concentrates, metal plating and
finishing sludges, industrial material, processed material, and/or
unprocessed material.
[0061] Prior to processing, selection of the Ni/Cr raw material is
determined by testing (100) to determine whether the Ni bearing
groups satisfy predetermined criteria. For example, the Ni/Cr raw
material is tested to determine whether a sufficient amount of
metals are present in the Ni/Cr raw material. The Ni/Cr raw
material preferably contains 5% by weight Ni and 5% by weight Cr,
and more preferably 10-20% by weight of Ni and 10-15% by weight of
Cr. The Ni/Cr raw material also can be tested to determine whether
any deleterious constituents (e.g., Hg) are present. It is
important to note that as economic conditions vary, improved
conditions (i.e., metal price increases, processing chemicals cost
decreases, etc.) may permit wider ranges of Ni/Cr content to be
economically processed by this invention. All economic conditions
as well as metals content (primary and secondary) must be
considered on an individual basis when determining the viability of
acceptance of the raw feedstock materials.
[0062] Ni/Cr raw material that satisfies the predetermined
acceptance criteria is then approved for processing (200). Any
material that does not meet the predetermined acceptance criteria
based on metal content and other constituent content and/or
economic considerations maybe designated as nonconforming material
(210). For example, when the Ni/Cr raw material contains mineral or
metal constituents which exhibit deleterious characteristics that
prevent the material from being safely or effectively processed,
the material may be rejected as non-conforming material or it could
be used as an ingredient in a formulation with other conforming
materials (220).
[0063] According to one aspect of the process, the nonconforming
Ni/Cr raw material is formulated and combined with other conforming
Ni/Cr raw material that has been found to satisfy the predetermined
acceptance criteria (300).
[0064] In yet another aspect of the process, Ni/Cr raw material
identified as non-conforming material may be combined as an
ingredient with other Ni/Cr raw materials to provide a
batch-formulation of material that does satisfy the predetermined
process criteria. For example, a first lot of Ni/Cr raw material
identified as "non-conforming" material when processed by itself
and unacceptable to be processed individually, may be formulated
with another raw material to provide a batch of Ni/Cr raw material
that does satisfy the predetermined criteria.
[0065] A slurry is then formed by adding to an aqueous medium the
Ni/Cr raw material batch or the formulated Ni/Cr material batch. In
one embodiment, the aqueous medium is tap water. In another
embodiment, the aqueous solution is any recycled water (940) or
water recycled from a previous cycle using the described method
(950 or 955). The Ni/Cr raw material present in the slurry at this
stage will be in an amount of 1-10% by weight, and more preferably
2-5% by weight of the slurry.
[0066] The slurry is adjusted to an alkaline pH (e.g., a pH of 12)
by the addition of a compound that accepts protons, for example
caustic soda (50% NaOH) (400). Cr is present in the alkaline slurry
in both the Cr(III) and Cr(VI) oxidation states. In its Cr(III)
oxidation state, Cr is in the form of a Cr precipitate such as
chromium hydroxide (Cr(OH).sub.3) or chromium oxide
(Cr.sub.2O.sub.3). In its Cr(VI) oxidation state, Cr is in an
alkaline soluble-form, such as chromate (i.e., a salt containing
the anion Chromic Acid (H.sub.2CrO.sub.4 or CrO.sub.4.sup.2-). The
Ni is present in the slurry in an insoluble form.
[0067] In order to separate the Ni in insoluble form from a Cr
precipitate, the alkaline slurry is treated with an oxidizer. The
oxidizer is preferably a permanganate (MnO.sub.4.sup.-) compound,
such as, for example, potassium or sodium permanganate. The
MnO.sub.4.sup.- is preferably added in excess. The solution
preferably has an Oxidation Reduction Potential (ORP) of +300 to
+400, which is preferably maintained for 1-3 hours and more
preferably for 2 hours so that a sufficient amount of
MnO.sub.4.sup.- can react with Cr in an insoluble form. The
oxidizer converts Cr(III) to its more soluble form of Cr(VI) to
form a chromate or dichromate solution. The reaction is exemplified
as follows:
[0068] for Cr(OH).sub.3:
2Cr(OH).sub.3+4MnO.sub.4.sup.-=2CrO.sub.4.sup.2++4MnO.sub.2+3O.sub.2
(1)
[0069] for Cr.sub.2O.sub.3:
2Cr.sub.2O.sub.3+8MnO.sub.4.sup.-=4CrO.sub.4.sup.2++8MnO.sub.2+3O.sub.2.
(2)
[0070] The chrome (Cr(VI)) compounds formed (e.g.,
CrO.sub.4.sup.-2/Cr.sub.2O.sub.7.sup.-2) are soluble, whereas the
MnO.sub.2 compounds are insoluble. By converting the Cr(III) in the
slurry to a more soluble form of Cr (i.e., Cr(VI)), the Cr can be
selectively leached from the slurry.
[0071] For example, a first and second oxidizer can be added
sequentially to the slurry. Oxidizers capable of converting Cr(III)
to Cr(VI), are relatively expensive. To lower the process cost, a
less expensive oxidizer may be first added to the alkaline slurry
(i.e., a first oxidizer). The first oxidizer is added in an amount
sufficient to react with extraneous organic and inorganic compounds
(e.g., compounds not containing Cr) present in the slurry. An
"amount sufficient` is preferably an amount wherein the first
oxidizer is added in excess as indicated by a potassium iodide or
starch test paper providing a color change when excess oxidizer is
present. The first oxidizer is preferably a hypochlorite, such as
calcium hypochlorite, ferrate, or ozone.
[0072] Once any extraneous organic and inorganic compounds have
reacted with the first oxidizer, a more costly oxidizer capable of
converting Cr(III) to Cr(VI) (i.e., the second oxidizer) can be
added. In other words, the first oxidizer may be regarded as a
"sacrificial" oxidizer that reacts with the extraneous organic and
inorganic compounds. This allows for a greater amount of the more
costly second oxidizer to react with the Cr of the Cr bearing
material present in the slurry. By doing so, smaller amounts of the
more costly second oxidizer will be required during the process,
reducing the process cost. The second oxidizer is preferably added
in excess to provide an ORP as discussed above. For example,
approximately two pounds of MnO.sub.4.sup.- can be added for each
pound of the first oxidizer that was added to the alkaline slurry
(500).
[0073] Once the reaction is complete, the slurry can then be
filtered (600) to obtain a filter cake containing Ni and insoluble
oxides such as MnO.sub.2 (610). The Cr remains in a Cr(VI) solution
(700) and can be optionally recovered as discussed below. Filtering
methods and devices known to those skilled in the art can be used
for this filtration step.
[0074] The filter cake containing Ni is optionally batched with
other filter cakes (620) previously obtained in accordance with the
method discussed above. The filter cake may then be further
concentrated (630) by dehydration using methods and devices known
to those skilled in the art.
[0075] The filter cake may also contain additional metals that were
present in the raw material and that may be recovered along with
the Ni. The other base, precious, and platinum group metals in the
filter cake include but are not limited to Ni, Cu, Co, Sn, Zn, Mo,
Mn, Pb, Cd, V, Ag, Au, Pd, Pt, Rh, Ru, Os, and Ir (i.e., third
metals).
[0076] The Ni concentrate and other metals obtained from the
process are optionally further separated by adding the Ni
concentrate and other metals to a smelter. Smelting is a form of
extractive metallurgy; its main use is to produce a metal from an
ore. Smelting uses heat and a chemical reducing agent to change the
oxidation state of the metal ore.
[0077] The resulting Cr(VI) solution (700) is preferably processed
in one of two ways. In one embodiment, the Cr(VI) solution is
processed (710, 720) into a chromium hydroxide filter cake (1000).
In another embodiment, the Cr(VI) solution is processed (750, 760,
780) to obtain a concentrated Cr(VI) solution or crystalline Cr(VI)
powder (2000).
[0078] When processed into a filter cake (1000), the Cr(VI)
solution is reduced from Cr.sup.+6 to Cr.sup.+3 to form Cr
hydroxide (710) by adjusting the pH of the Cr(VI) solution to an
acidic pH (e.g., 1.0 to 2.0) with an acid, such as sulfuric acid
(H.sub.2SO.sub.4) or nitric acid (HNO.sub.3) (710) and then adding
a reducing agent such as sodium metabisulfite
(Na.sub.2S.sub.2O.sub.5) to the solution. The resulting solution is
maintained with stirring for preferably 30 minutes to 2 hours, and
more preferably 1 hour to assure that a sufficient amount of
reducing agent reacts with the Cr. The reaction is exemplified as
follows:
2CrO.sub.4.sup.-2+2Na.sub.2S.sub.2O.sub.5=2Cr.sup.+3+4NaSO.sub.4+O.sub.2-
. (3)
[0079] Following the Cr reduction, the pH of the solution is raised
to form an alkaline solution (e.g., having a pH of 9.0). The
solution is preferably raised by adding a compound that accepts
protons, for example caustic soda (50% NaOH) (710). The reaction is
exemplified as follows:
Cr.sup.+3+3NaOH=Cr(OH).sub.3+3Na.sup.+. (4)
[0080] A Cr hydroxide precipitate is formed (710) and is preferably
recovered in the form of a filter cake. In a preferred embodiment,
the solution Cr precipitate is recovered with a filter press (720)
to produce a chromium hydroxide filter cake (1000). Filtering
methods known to those skilled in the art can be used for this
filtration step.
[0081] The chromium hydroxide filter cake (1000) may contain
elevated concentrations of sulfate resulting from the production of
NaSO.sub.4 during the previous chrome reduction reaction. Water
soluble NaSO.sub.4 is retained in the interstitial waters of the
filter cake. A low sulfate chromium hydroxide product is more
commercially desirable, therefore the chromium hydroxide filter
cake (1000) containing elevated concentrations of sulfate can be
optionally further processed by re-slurrying (1010) the chromium
hydroxide filter cake (1000) with a solids solution (e.g. 10% solid
solution) to leach out the sulfate, and recovering a second
chromium hydroxide filter cake with a filter press (1020). Water
soluble sulfate compounds and other water soluble compounds are
contained in the filtrate and removed from the filter cake.
[0082] An alternate sulfate reduction method involves "washing"
(1040) the initial filter cake, while still contained in the filter
press, by passing a sufficient volume of fresh water through the
press to reduce the sulfate content to a desirable level. This
alternate washing procedure is preferably used when lesser amounts
of sulfate need to be removed.
[0083] These optional slurrying and filtration steps produce a
chromium hydroxide filter cake (1030) with a higher purity.
[0084] The resulting filtrate may then be further treated (800) and
recycled (950) as the aqueous solution in the slurrying step
(400).
[0085] As noted above, the Cr(VI) solution may be processed into a
concentrated Cr(VI) solution or powder (2000). The Cr(VI) solution
may be concentrated by ion exchange (750) and/or concentrated by
evaporation (780). In this aspect of the invention, the Cr(VI)
solution is either directly (740) subjected to an
evaporation/crystallization process (780) from the selective
leaching process (700) or alternatively, passed from the selective
leaching procedure (700) through an ion exchange column (750) to
selectively remove the Cr. The Cr(VI) is loaded onto column by
passing the Cr(VI) solution over the column. The aqueous fraction
exiting the column is substantially free of Cr and can be re-used
(955).
[0086] When the Cr(VI) has been loaded onto the column (750), the
ion exchange resin may be regenerated by eluting the resin with a
hydroxide solution, such as a 5% NaOH solution (760). The eluted
Cr(VI) solution is then preferably further concentrated. In one
aspect of the invention, the eluted Cr(VI) solution is concentrated
5-10 fold (760).
[0087] The eluted Cr(VI) solution may then be evaporated (780) with
the use of a heating source such as waste heat exchange (770) or a
heater (775) to obtain a concentrated Cr(VI) solution or
crystalline Cr(VI) powder (2000). Evaporating and drying methods
and devices known to those skilled in the art can be used for this
evaporation step.
[0088] In yet another embodiment, the present invention relates to
a composition produced by the above-identified method, wherein said
composition preferably comprises Ni or Cr.
[0089] The foregoing description of the invention has been
presented describing certain operable and preferred aspects. It is
not intended that the invention should be so limited since
variations and modifications thereof will be obvious to those
skilled in the art, all of which are within the spirit and scope of
the invention.
* * * * *