Note: Descriptions are shown in the official language in which they were submitted.
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IUIETHOD FOR RECOVERY OF NONFERROUS, RARE AND PRECIOUS
1VIETALS FROM ROBUST MINERALS
The method is referred to hydrometallurgy process and it serves for
recovery of nonferrous, rare and precious metals from robust (hatd to process)
minerals, whirh may contain natural carbon or other robust compounds.
Very frequently the well-known techniques for recovery of nonferrous,
rare and precious metals from robust minerals containing carbonaceous
component or other robust compounds, do not provide satisfactory performance.
First of all it stei'ns from high resistame to o~ddation and high sorption
activity of carbonaceous cornponent of the minerals involving great loss of
nonferrous, rare and precious inetals with solid residue of processing.
In the framework of the present method ores and concentrates containing
organometallic, cluster, colloid and otlier chemical and composite compounds,
hindering the process of useful components recovery, should be classified
among
technologically robust minerals.
Hence, during cyani.dation of robust carbonaceous ores and concentrates,
for instance, no traces of precious metals are detected in solution in some
cases,
i.e. precious metal complexes formed as a result of interaction with cyanide
are
completely adsorbed by carbonaceous component in the mineral. Cyanidation in
the presence of ion-exchange resins and carbons, as well as using sorption
passivators like kerosene or apolar liquids, somewhat improves the recovery of
precious metals but not infrequently its processing characteristics are as
low.
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Methods for carbonaceous ore leaching arc described in the book "Precious
Metals Metallurgy" by Maslenitsky et al, published in Moscow in. 1987, pages
288-291 as follows: "... in some ores carbonacepus substances feature
different
settling capability, which complicates largely the cyanidation process. ...
During
cyanidation of carbonaceous ores kinetics of precious metal transfer to
solution is
determined by the ratio of two opposite processes, i.e. dissolution and
sorption.
.. .Certain rate of leaching ... promotes maximum extraction .., in the course
of
carbonaceous ores cyanidation. The rate of sorption depends also on
carbonaceous
substance surface area. Optimal degree of material grinding should be
maintained.
Thus, one of the methods of carbonaceaus ore direGt cyanidation consists iri
arrangement of usual cyanide process, observing the optimal degree of grinding
and period of contact between the ore and cyanic solution. Another inethod...
consists in arrangement of leaching in several successive stages with solution
renewal at each stage. Adsorption capacity of carbonaceous substances may be
somewhat decreased by preliminary treatment of ore using flotation oils,
kerosene, bituminous coal sublimation products and some other reagents....
However, the efficiency of the method is not very high, ... Cyanidation of
carbonaceous ores using water-soluble organic nitriles, their actual
applications
not being tiltimately ascertained, is of interest. Sorption leaching proved
the most
efficient method for cyanidation of carbonaceous ores and concentrates ".
Attempts to reduce sorption activity of carbon-containing raw materials by
thermal treatment in vacuum (for removing unsaturated oxides from carbon)
failed to be widely used due to problems in hardware implementation, high
costs
of the process and low process performance.
In monograph "Solvents for Gold and Silver in Hydrometallurgy" by
Mineev G.G. and Papchenko A.F. published by "Metallurgiya" (Metallurgy)
Publishing House in 1994 in Moscow some problems arising from application of
the known methods of leaching are mentioned in pages 192-205: "Bacterial
leaching involves problems of intracellular metal accumulation, low
performance
of subsequent sorption leaching, build-up of biomass on the equipment".
Leaching
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by heterotrophic microorganism metabolism products and amino acid solutions
yielded rather low results in reference to recovery into solution. Filtration
leaching
of gold-containing source materials necessitates recycling of productive
solutions.
That is why the latter shall be proces'sed in situ, while methods of gold
recovery
from solutions shall feature high efficiency, simplicity of hardware
implementation and no pollution of gold-free filters by other components.
Hence,
sorption biochemical leaching was chosen as the basic method for gold recovery
from ores.
Passivation of carbon sorption activity using bacteria active life products
(bacterial leaching) necessitates special fermenters for growing bacteria,
fine
grinding of the material, strict observance of teniperature and chemical
conditions,
long duration of the process. In some cases, when there are greb.t amounts of
As
and Sb, for instance, bacterial leaching proved inipossible due to bacteria
poisoning with heavy metals. Bearing in mind the above-mentioned, bacterial
leaching has not been used extensively for processing robust carbonaceous
minerals.
Chlorination method of precious metal recovery from ores, consisting in
ore treatment by aqueous solution of hypochlorite, iron ions and acid at
elevated
temperature, is its immediate analog (prior art), solving the problenx of
precious
metal recovery from robust minerals, which is described in US Patent No.
4439235 of 14.06.1982, Int.Cl,': C22D 3\00, U.S. Cl.: 75\101 R. After
filtration
the solid residue is treated repeatedly by hypochlorite and iron-ion aqueous
solutions at pH=7. Compounds of precious metals are extracted from liquid
phase.
The prior art mentioned and the stated technical approach have the
following in comnlon: treatment of robust carbon-~containing mineral with
oxygen-containing oxidant and subsequent extraction of precious metal
compounds from liquid phase.
Great consumption of hypochlorite for mineral oxidation, explained by the
fact that hypochlorite decomposition, especially at elevated temperature,
proceeds
according to chlorates and chlorides formation mechanism, can be mentioned
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among drawbacks of the method described. Meanwhile, hypochlorite and its
disproportionation products do not take part in oxidation of precious metals
and
their transfer to solution:
2NaClO + NaCIO = NaC103 + 2 NaCI
High oxidizing activity of hypochlorites combined with their
thermodynamic instability results in a very rapid decrease in effective
oxidant
concentration in the slurry, giving rise to high cost of processing and
insufficient
degree of precious metal recovery from minerals.
This invention is aimed at increasing the recovery of nonferrous, rare and
precious metals from robust minerals with simultaneous reduction of processing
costs.
The objective is attained, as the method for recovery of nonferrous, rare
and precious nietals from robust minerals envisages the processing of robust
carbon-containing minetals by oxygen-containing oxidant with subsequent
extraction of precious metal compounds fxom liquid phase, moreover, the
treatment of robust carbon-containing minerals by oxygen-containing oxidant is
perfornled in the presence of reducing agents featuring donor-acceptor
properties,
which are manifested in the fact that at the first stage of chemical reactions
the
reducing agents give their electrons to oxygen-containing oxidant and, as a
result,
form a stronger oxidant than the initial one, in the from of short-lived
radicals and
intermediate oxidation products of donor-4cceptor reducing agents, which are
oxidants, as well.
According to the method proposed, the treatment of robust Garbon-
containing minerals by oxygen-containing oxidant is realized in the presence
of
reducing agents featuring donor-acceptor properties. Donor-acceptor properties
of
the reducing agents used are pronounced in the fact that at the first stage of
chemical reactions the reducing agents give their electrons to oxygen-
contairiing
oxidant and as a result form a stronger than initial oxidant, in the form of
short-
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lived radicals and intennediate oxidation products of donor-acceptor reducing
agents, which are mild and selective oxidants.
TQchnically, the essence of the invention proceeds from specific features
of using oxygen-containing compounds as oxidants for robust minerals.
Introduction of the donor-acceptor reducing agents into hydrometallurgical
process permits:
- first, directing the decomposition of oxygen-contailiing oxidants in line
with the
most favorable mechanism for oxidation of nonferrous, rare and precious
metals;
- second, prolonging the action of oxidants by mediating their oxidizing
potential
via the reducing agents oxidation products, which are milder and more
selective
oxidizing agents;
- third, making use of compleidng capability of the reducing agents for
overcoming kinetic and electrochemical difficulties in dissolving nonferrous,
rare
and precious metals and stabilizing the dissolved precious metals in liquid
phase;
- fourth, transforming the intermediate compounds formed as a result of
oxy~ygen-
containing oxidant disproportionation into short-lived "fast radicals",
permitting
oxidation of orga~..nolnetallic, cluster, colloid and other chemical and
composite
compounds, which increases essentially the utilization factor of robust
minerals.
Existence of the above-mentioned mechanisms of chemical interactions is
confirmed by the following theoretical and experimental data:
1) In solutions of oxygen-containing oxidants without donor-acceptor reducing
agents the decomposition of oxidants proceeds by the following reactions:
C12 + H20 = HCl + HCIO
2HC1O=2HC1+02
MeCIO + 2 HC1O = MeC1O3 + 2 HCl
H2S208 + H20 = HaSOs + H2S04
H2S05 +H20 = HZSO4+ H202
H2SO5 + H202 = H2S04 + Oz + H20
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It follows from the reactions presented that as a result of decomposition of
oxygen-containing oxidants, not involving donor-acceptor reducing agents, the
decomposition and disproportionation products are accumulated in solution
along
with evolution of gaseous oxygen, which are not effective oxidants under
normal
conditions. Accordingly, it gives rise to high consumption of oxidants and low
performance of recovery process.
2) In the presence of donor-acceptor reducing agents the oxidation potential
of
oxygen-containing compounds is actually entirely used for the formation of
short-
lived radicals and reducing agent oxidation products. The following reactions
take
place as a result:
2NaNO2 + Cla = NaNO3 + NOCl + NaCl
NaNOz + Cl2 = N02C1 + lNaCl
Cl2+H2(,1=I-ICI+I-ICIO
HCI + NaNOz = NaCl + HN02
4NaNO2 + 4HC1O = 4NaCl + 2H20 + 20 + 4N02
2S02 + Ciz = 2SO2C1
1-I2SO4 + HCIO + HCI = .H2S 5C12
Using NaNO2 and SO2 by way of example, it follows from the reactions presented
that interaction between the Cl2 - HCIO oxidant and donor-acceptor reducing
agents gives rise to formation of many products, i.e. NaNO3, NOCI, N02C1,
HN02, SO2Cl, 02, H2S05C12, etc., each of them can serve an independent
oxidant for nonferrous, rare and precious metals.
Meanwhile, the oxidation potentials developed by the compounds during
reduction to lower valency states, fall within a wide range relative to normal
hydrogen electrode. Actually all the substances feature complexing properties
and
form compounds with nonferrous, rare and precious metals, required for the
process. The presence of various compounds featuring diverse electrochemical
and complexing properties during oxidation of nonferrous, rare and precious
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metals permits increasing thermodynamic probability of the metals oxidation
and
their transfer to solution.
Compounds of higher oxidation state, e.g. chlorates, perchlorates,
persulfates, perbromates, other oxygen-containing oxidants and their
derivatives
have great bound chemical energy, but chemical energy cannot be used for
oxidation of nonferrous, rare and precious metals owing to stability of
chlorates
and perchlorates as compounds and their low chemical activity.
In the invention proposed oxidants featuring the highest valency of acid
residue atom, for instance, chlorates, perchlorates, persulfates, perbromates,
other
oxygen-containing oxidants and their derivatives are used as oxidants in the
presence of donor-acceptor reducing agents. As a result, the donor-acceptor
reducing agents give rise to the formation of radical, i.e. oxygen superoxide,
atomic oxygen and other highly reactive compounds, including the reducing
agents oxidation products, which permits effective oxidation and dissolution
of
nonferrous, rare and precious metals contained in the minerals, i.e.:
2NaClO4 + S(lz = Na2SO4 + 2 C102
NaNC)a + HCI = HNC2 + NaCI
2HN02 = H20 + NO2 + NO
NaCl 4 + NO = NaNO3 + C102
2HC103 + NaN 2 = NaNO3 + 2CI 2 + H20
Na2S2Q8 + 2N = 2NC?2 + Na2SO4 +SO2
C102 + 3NO2 = N205 + C1N 3
It becomes obvious from the reasoning above that the proposed method for
recovery of precious metals differs from the known ones, as robust minerals
are
treated with oxygen-containing oxidants in the presence of reducing agents
featuring donor-acceptor properties. Thus, the proposed method complies with
the
"novelty" criterion.
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Comparison of the approach proposed with the prior art and other
approaches in this field of engineering pennitted revealing the signs, making
the
proposed approach different from the prior art, moreover, the differences
considered are implicit, which suggests conclusion about compliance of the
approach proposed with the "invention level" criterion. The approach proposed
has industrial applications.
Examples of specific applications for the process proposed:
Example No. 1.
Hydrometallurgical oxidation was realized using ore featuring the
following mineral composition:
a) non-metallic minerals
siderite - 18.2%, calcite -1.0 10, quarkz - 8.3%, kaolin - 4.5 %,
chlorite -1.8%, albite -1.0 /u, hydromica - 1.0%, apatite - 0.3%;
b) ore mineral
goethite, limonite - 61.5%, pyrite -1.2%, chalcopyrite - 0.85%,
bornite 0.2%, covellite 0.1%.
The ore contained gold 7.4 g/ton ore, platinum 56 g/ton ore, palladium 12
g/ton
ore, and silver 150 g/ton ore, as well as copper 0.7% and cobalt 0.2%.
The ore, its amount 1 kg, was subjected to hydrometallurgical oxidation in
hydrochloric acid solution, its concentration 100 g per liter, in liquid-to-
solid ratio
(L:S) = 3:1, at a temperature of 80 C with intense agitation.
Ammonium persulfate (NH4)2S20s was used as oxidant in the amount providing
concentration of 10 g per liter, which was introduced into the slurry
immediately
after heating to assigned temperature. Check sample was agitated in parallel
with
the basic one without addition of donor-acceptor reducing agents.
Solution containing 10 g/l of sodium nitrite NaNO2 and 10 g/l of sodium
sulfite
Na2SO3 was introduced gradually into the basic sample. The feed rate depended
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on gas evolution intensity. Altogether 100 ml of solution containing donor-
acceptor reducing agents was consumed in 30 minutes. Hence, 1 gram of NaNOz
and 1 gram Na2SO3 was consumed per total amount of the oxidant equal to 30
grains.
The solutions prepared and solid residue were analyzed by atomic-
absorption and assay analyses for ascertaining the extraction of nonferrous
and
precious metals into solution.
In the checlc sample (without addition of donor-acceptor reducing agents)
the extraction into solution made up:
Copper - 73%, cobalt 68%, silver 57%, gold 64%, platinum 31 /0;
palladium 47% of their content in the sample.
In the sarnple witll donor-acceptor reducing agents metal eiitraction into
solution amounted to:
Copper - 98.5 1 , cobalt 97%, silver 94%, gold 98.3 /o, platin.un2. 94%,
paliadium 97%.
The results suggest that the use of donor-acceptor reducing agents
increases essentially the extraction of nonferrous a.,nd precious metals from
robust
minerals.
Example No. 2.
Hydrometallurgical oxidation was realized using ore featuring the
following mineral composition:
a) non-metallic minerals
siderite - 12.2%, calcite - 7.0%, quartz - 37.8%, kaolin - 3.7 %,
chlorite - 2.8%, albite - 2.0%, hydromica - 12.0%, apatite - 0.7%,
carbonaceous matter 4.5%:
b) ore minerals
goethite, limonite -11.5%, pyrite - 3.2%, pyrrhotine - 2.5%,
arsenopyrite - 0.1%.
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The ore contained gold 3.4 g/ton ore, platinum 2.6 g/ton ore, palladium 3.2
glton
ore, and silver 5 g/ton ore.
The ore, its amount 1 kg, was subjected to hydrometallurgical oxidation in
hydrochloric acid solution, its concentration 10 g per liter, at L:S = 3:1, at
a
temperature of 40 C with intense agitation.
Sodium hypochlorite NaClO was used as oxidant in the amount providing the
concentration of 5 g/l, which was introduced into the slurry immediately after
heating up to the assigned temperature. The check sample was agitated in
parallel
with the basic one without addition of donor-acceptor reducing agents.
Solution containing 10 g/l of sodium nitrite NaNO2 was introduced gradually
into
the basic sample. The feed rate depended on gas evolution intensity.
Altogether
200 ml of solution containing donor-acceptor reducing agent was consumed in 30
minutes. Hence, 2 grams f Na,N02 ws,s consumed per total amount of the
oxidant
equal to 15 grams.
The solutions prepared and solid residue were analyzed by atomic-
absorption and assay analyses for ascertaining the extraction of nonferrous
and
precious metals into solution.
In the check sample (without addition of donor-acceptor reducing agent)
the extraction into solution made up: silver 37%, gold 52%, platinum 21%,
palladium 37% of their content in the sample.
In the sample with donor-acceptor reducing agents metal extraction into
solution amounted to:
silver 87%, gold 92.3%, platinum 74 fo, palladium 87%.
The results suggest that the use of donor-acceptor reducing agents
increases essentially the extraction of nonferrous and precious inetals from
robust
minerals.
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Example No. 3.
Hydrometallurgical oxidation was performed using gravity c6ncentrate featuring
the fol.lowing cheznical composition: ,
SiO2 - 23%, A1203 - 5.6%, Fe (total) - 28 10, S (total) - 36%, crystallization
wa.tei' -1.34%, CaO -1.12 !o, MgO - 0.8%.
The concentrate contained gold 378 g/ton ore, platinum 47 ,g/ton ore,
paIladium 126 g/ton ore, and silver 2480 glton ore, as well as 3.8a/o of
nickel and
2.4% of cobalt.
The concentrate in the amount df 1 kg was subjected tb hydrometallurgical
oxidation in hydrochloric acid solution, its concentration 70 g per liter, at
L:S =
2:1, at a temperature of 70 C under intensive agitation.
Ammonium percblorate (NH)2C1207was used as oxidant in the amount ptoviding
concentration of 10 g per liter, and sodium iodate Na103 in the amount
providing
concenUation of 5 g per liter, were introduced io.to the slurry immediately
after
heating to assigned temperature. The check sample was agitated in. parallei
with
the basic one without addition of donor-acceptor reducing agents.
Solution containing 10 g/1 of sodium sulfite 1rTaISO3 and 5 g/l sodium
thiosulfatt NaZS203 was gcadually introduced in the basic sample. The feed
rate
depended on gas evolution intensity. In tota1300 ml of solution containing
donor-
acceptor tedwing agents was co:nsumed in 45 ininutes. So, 3 grams of Na2SO3
and 1.5 gra.ms of Na2SZO3 were consum~d per total amount of oxidants equal to
45 grams.
The solutions prepared and solid residue were analyzed by atomic-
absorption and assay analyses for ascerta.ining the extraction of nonfersous
and
precious metals into soiution.
In the cbeck sanlple (without addition of donor-acceptor reducing agents) the
efctraction into solution made up:
nickel - 63%, cobalt - 57%, silver - 48%, gold - 63%, platinum - 42%,
pallad;um - 54% of their content in the sample.
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In the sample with donor-acceptor reducing agents metal extraction into
solution
amvunted to:
nickel - 98.5%, cobalt - 95%, silver - 89%, gold - 94%, platinum - 89%,
palladium - 92%.
The results suggest that the use of donor-acceptor reducing agents
increases essentially the extraction of nonferrous and precious metd.i.$ from
robust
minerals.
