Note: Descriptions are shown in the official language in which they were submitted.
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POLYMER SORBENT FOR ~ON RECOVERY PROC'F..~.~F..C
~ he present invention relates to a process for the removal of ions from
slurries, pulps or other dispersions of solids in liquids. In particular, the present
S invention relates to a process for the selective removal of ions from dispersion of
solids in solutions and also relates to coarse open cell polymeric foams which
support ion ~Y h~nge sites.
The selective removal of ions from solution is an important process in many
10 industries. In conventional ion recovery or removal processes ions, are removed
from solutions by the use of processes such as ion çyrh~nge onto solid beads or
fibres, membrane processes, activated carbon adsorption, preririt~tinn> solvent
extraction, ion flotation and the like. The removal of ions from solutions ~,vhich also
contain solid materials dispersed throughout such as in slurries, pulps and the like
15 is more difficult. The applic~tion of ion rY~h~nge resins and activated carbon is
widely practiced throughout many industries inrl~ ing the minerals processing
industry where selective removal of ions from slurries is necessary and has become
the method of choice in the recovery of gold by cy~nicl~tion and in the recovery of
uranium as the uranyl slllph~te, for eY~mple.
In order to achieve good recovery of desired ions from a solution it is
desirable to provide a uniform distribution of solid sorbents such as ion eyrh~nge
resins or activated carbon in the solution. This requires that the density of the solid
sorbent be close to the density of the solution otherwise the added ion ~Y~h~n~e25 beads or the activated carbon will sink or float within the solution. Good recovery
of ions from solutions having solid materials dispersed therein also requires that the
sorption medium is uniformly distributed throughout. In order to achieve efficient
recovery of the desired ions it is necessary to provide a sufficient concentration of
solid sorbents in the solution, whether or not solid materials are dispersed in the
30 solution. The concentration of solid sorbents is generally limited by the presence
of solid particles in solution. For .oY~m~le, the density of the solid sorbents
desirably matches or at least a~rnxii--~tçs the pulp density which is only
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determined by the ratio of mass of the solid particles to the solution. The density
of the solid particles cannot be modified, nor is it generally possible to significantly
change the density of the solution.
S Extractive metallurgical terhniques generally seek to obtain metal values
from ores or concentrates. In order to achieve separation, the solids may be
introduced into a reactor together with requisite lixiviants to dissolve the metal
values and in doing so, typically produces a slurry. In such processes, other ions
may also be brought into solution. Thus, a material which can selectively removeor recover the desired ion is added to the slurry usually in the form of a solidsorbent dispersed in the slurry. Alternatively, the sollltion cont~ining the dissolved
ions is separated from the solid materials and the metal ions are then recovered or
removed from the clarifled soll~tion
The m~imi7~tion of plant capacity in such processes requires a high
proportion of solids in the sld~ cor~,istent~w,th good rn~r.g ar.d pllmping ~n.dh~n~lling properties. Thus, in order to attempt to distribute the solid sorbentsuniformly throughout the slu~y, high intensity mixing is often used. This rapid
shearing action generated in the reactor can lead to destruction of the active solid
sorbent by attrition and breakage. This breakage can result in the loss of valuable
ions into the discharge from the plant along with the slurry.
The solid sorbent is typically recovered from the slurry or from the solution
by screening. In the case of ion eyrh~nge resins the particle size of the resin is
selected in a size range which is generally fine enough to exhibit desirable loading
and elution kinetics. Fine ion eyrh~nge beads are more difficult to recover fromthese pulps because the screen opening size employed must be greater than the
particles m~king up the slurry, but smaller than that of the ~m~llest ion elrrh~nge
beads. For example, in U.S. Patent 5,198,021 the ion e~rh~nge resin bead size ispreferentially recommended to be between 6 and 12 mesh. "Blinding", or screen
blocking can thus readily occur.
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Additionally, ion ~ h~n~e resin beads suffer from the problem of osmotic
shock. Thus, swelling and shrinkage of the ion .oYrh~nge resin bead during loading
and stripping of the metal ions cont~in~cl thereon can lead to resin breakage.
We have now found that solutions cont~ining solid materials dispersed
therein may be passed through coarse open cell polymeric foams having ion
to~r~h~nge sites incorporated into the open cell polymeric foam and the selective
removal of ions from solution may be achieved. Accordingly, there is provided a
process for the selective removal of ions from a solution having solid materialsdispersed therein comprising passing the solution having solid materials dispersed
therein through a bed of coarse open cell polymeric foam having ion ~Y ~h~nge sites.
Suitable coarse open cell polymeric foams inc~hlde coarse cell polyurethanes
and ~l ef~;l ably coarse cell retic~ te~l polyurethanes. Polyurethane-based polymers
are recognised for their high abrasion resistance. These polyurethane-based
polymers have also been modified to incorporate ion ~Y~ h~ngin~ sites as described
in PCT/AU93/00312 and PCT/AU94/00793 incorporated herein by reference and
also include any polymeric resin which has been provided with a suitable
function~lity for the sorption of the desired ion either by interpenetration by a
second polymer (such second polymer typically as described in South African Patent
ZA 89/2733 and Canad. Patent Application 2,005,259) with or without further
chemical modification, polyurethane polymer chemical modification, organic
extractant impregn~tion such as described by Lin et al in U.S. Patents 4,814,007,
4,895,597, 4,992,200, 5,028,259, U.K. Patent G.B.2,186,563A and P~-l WO93/19212
and Virnig in U.S. Patents 5,198,021 and 5,340,380 or known to those skilled in the
applic~tion of liquid ion ~Yrh~n~e extr~rt~ntc, etc. These polyurethane-based
polymers can be produced in a variety of forms such as beads or fibres, but can also
be expanded to produce flexible, semiflexible and rigid foams. Blocks of foams
several cubic metres in size may be produced. Larger blocks can be pro~ e-l by
well established bonding processes. These blocks of foam can be cut to any suitable
shape and size dependent upon the requisite application. Alternatively, blocks of
foam can be produced to the desired size and shape by pouring the liquid foaming
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reagents into a suitable mould and after the reaction has reached a suitable degree
of curing, removing the item from the mould.
The polyurethane foams are preferably flexible and can either be polyester-
5 based or polyether-based. Polyether-based polyurethane foams are generally
preferred because of their ~lemon~trated improved chemical resi~t~n~e over the
ester foams. Huw~vel, for some specific applications ester foams may possess
suitable properties. The polyether-based foams may be produced by the reaction
under controlled conditions of a suitable polyol or blend of polyols with one or10 more diisocyanates in the presence of catalysts, cell control agents and, if required,
fillers, flame retardants, etc. The polyols are usually based upon the reaction of di-
or higher functional materials with ethylene oxide (EO), propylene oxide (PO), or
mixtures of these two oxides. For flexible polyurethane foams, gly~;eli~le is one
preferred starting material and this is reacted with EO and/or PO to produce a
15 polyol with a molecular weight generally in the range of 3000 to 6000. The
diisocyanate is generally toll-~ ne diisocyanate (T~I) or diphenylmethane-4,4'-
diisocyanate-based materials (MDI), but is not limite~l to these two isocyanates.
Polyurethane foams may be "retic~ ted", that is, most or all of the residual
20 "windows" or cell walls are removed by such processes as have been described by
Volz in U.S. Patent No. 3,171,820 and by Green in U.S. Patent Nos. 3,175,025 and3,175,030 and which are well known to those skilled in the pro~ ction or fabrication
of polyurethane foams.
It has been found that these reticnl~te-l polymeric polyurethane foams are
able to have solutions c~nl~lisi lg solid materials, such as pulps or slurries similar
in composition to those found in the minerals processing industry very rapidly
pumped through them without any indication of blorking Fine-celled flexible
polyurethane foams under the same conditions are rapidly blocked by the solid
materials thus ~lcvt;lltillg the slurry from continlling to flow freely through the
polyurethane foam.
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The selection of cell size in the polymeric foarn is depen~lent on the largest
particle size of the solid materials contained in the solution. It is ~lef~:lled that the
cell si_e be at least three limes the largest particle size of solid materials in the
solution. In the mining industry slurries cont~ining metal ions in solution in
5 addition to solid particulate ore residues are common and we have found it
preferable that the polymeric foam has a cell size in the range of from 45 cells per
linear inch (180 cells per 100mm) to less than 15 cells per linear inch (60 cells per
100mm). It is desirable to select a cell size wherein the surface area of the
polymeric foam is m~imi7ecl without resulting in blocking of the foam with the
10 solid particles from the sollltion
The introduction of these coarse open cell polymeric foams having ion
~h~nging sites into a reactor in the form of a fixed-bed such as the p~t~hllc~c used
in the gold cy~nid~tion industry provides a process for ensuring that the ion
15 f~Yrh~n ing material is much more u~irollllly distributed throughout the slurry or
pulp and has a large ~co.ccible surface area. This means that the sol-~tion is able
to better contact the ion ~ h~nging sites, uv~rcollles screening problems, reduces
the need for intensive mixing and reduces the loss of valuable metal ions to thetailings dischOEge.
Beds of coOEse open cell polymeric foams cont~inin~ the desired lig~n-ls may
be housed in suitably co~ ucted vessels. Such vessels may be designed to allow
liquid cont~ining solid materials to pass through the polymeric foam either by
gravity or by ~ i . .g or by other means and provides an impl uv~:d recovery system
25 for the desired ions. Solutions cont~ining from less than 15% of solids to over 50%
by weight of solids and vOEying in pOEticle size from less than 45 micron to greater
than 150 micron have been contilluously pumped or passed through coarse open
cell polymeric foams.
Flexible polymeric foams may be able to undergo repe~ted flexing and
th~l~role the additional possibility of applying a me~h~nic~l pulsing action to the
foam bed is achieved.
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The polymeric foam comprises ion loxrh~nge sites. These sites may be
provided in the initial manufacturing process of the polymeric foam or may be
provided by modification of the foam after its initial manufacture. The selection
of a~l!.u~liate functional groups at the ion eY~h~nge sites allows the selective5 recovery of a broad range of ions in solution. For .ox~mrle the polymeric foam may
have ion .ox~h~nge functionality for the selective removal of heavy metals in~ cling
arsenic, c~lmil-m, chromium, iron, zinc and mercury; precious metals in~ ling
gold, silver, rl~timlm, p~ llm, rhodium, iridium, ruthenium and o~mi~lm; other
anions and cations including h ~ les, sulfates, nitrates, cyanides, thiocyanates,
10 cyanogen, carbonates and phosphates.
In certain metal ion recovery processes, oxygen may be required as part of
the chemical reaction, for ~x~mrle in the dissolution of gold in oxygenated ~lk~linto
sodium cyanide solution. These coarse and open cell polymeric foams will allow
15 the passage of both the solution, slurry and if required, air, oxygen or other gas.
The polymer foam in some cases may also assist by hll~luvillg the distribution of
the gas throughout the solution, pulp or slurry.
In a second aspect the present invention provides an ion-selective coarse
20 open cell polymeric foam as hereinabove described in which the cell size is
sufficient to allow solutions having solids dispersed therein to pass through said
foam.
The present invention will be hereinafter described with lefe~ellce to
25 retic ll~tecl polyurethane foams, huw~v~ , it will be understood that other coarse
open cell polymeric foams will be equally suited.
In the gold industry, the loss of gold cyanide by adsorption of the
aurocyanide anion onto the surfaces of clays, ~ rhi~le minerals, carbonaceous
30 materials, etc. is well recognised and has been termed "preg robbing". The shorter
the path length which a metal ion needs to travel to be sorbed by the deliberately
introduced selective metal ion sorbent, the less the O~Ol ~ y for "preg robbing"
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to occur. Also, it has been proposed that dil~lting the pulps to low solids content
such as 15% solids content and lower, can also reduce "preg robbing" and thus
increase metal ion recovery. The described fixed-bed of ligand-modified reti~ll~ted
polyurethane foam provides a short path length for the metal ions to travel prior
S to sorption. Additionally, these modified polymers do not catalyse the o~ tion of
the sodium cyanide to cyanates or cyanogen as is the case for activated carbon.
The slurry pumped to tailings normally contains cyanide, as "free" cyanide or WAD
(weak acid dissociable) cyanide, thiocyanates, etc. Thus, the tailings pondage
contains anions which are toxic to h~lm~n, animal and bird life and therefore
10 represent a significant el,vilo~ e-nt~l hazard. The presence of these toxic anions
maywell prevent the return of these sands underg~oulld as mine fill because of the
potential for the toxic ions to enter the water table.
An example of the industrial application for this technology would be as an
15 alternative for the process as described by Coltrinari in PCT W 087/00072 or the
well known AVR and Cyanisorb processes for the recovery of free and WAD
cyanide from the CIP or CIL slurry prior to its depositlon in a tailings dam. Inthese processes, the slurry is acidified to provide a sol~ltion pH generally between
5 and 8 in order to convert the cyanide species to HCN. Large volumes of low
velocity air are then passed through the pH-adjusted tailings in a packed tower to
volatilise the HCN. The HCN gas is readsorbed in an ~lk~lint- solution and
returned to the CIP/CIL circuit. The stripped slurry must have its pH readjustedto 10 to 11 prior to deposition in the t~ilin~ dam. This process clearly suffers from
a number of disadvantages: the requirement for twice adjusting the pH of the
entire slurry and the use of very large volumes of air to vol~tili~e the HCN formed.
The application of a fixed bed of a suitable reticulated polyurethane foam
for cyanide recovery offers a number of economic and kinetic advantages as will be
described. In the presently described process, the free cyanide is COllv~lled to a
30 WAD cyanide such as by the tre~tm~nt of the slurry with a metal or soluble metal
salt in particular with copper or zinc ~lllph~te The slurry then passes through a
suitable bed of a selected reti~l~te~l polyurethane foam which has been modified
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to contain a suitable ligand. The complex metal cyanide ion is rapidly adsorbed
onto the polyurethane foam and the cyanide-depleted slurry passes to the tailings
dam without the need for any pH adjustment (other than that which may be
required by any particular mining or ellvi~ol"llental guvell~.llent regulation
5 applicable to that mine). The loaded polyurethane foam column is acidified to
generate HCN gas which is adsorbed in an ~lk~line solution. A suitable courier gas
such as nitrogen or air may be required. The acid solution may be reused for
further stripping. Thus, a closed circuit plant can be ~lçcign~l in which much
cm~ller volumes of air and sol-ltionc are required. Alternatively, if a ligand capable
10 of sorbing the WAD cyanide has been used and which is capable of being elutedat high pH, then the WAD cyanide can be stripped from the column. HCN gas can
be generated from the strip solution and sodium cyanide formed or alternatively
sodium cyanide reformed by electrolysis in a suitably ~ cignecl electrolysis cell.
A further application for the technology would be for the removal of soluble
salts in lignite and other coals or for the removal of dissolved metal salts from soils
in soil remediation processes, again, by allowing the slurry cont~inins~ the metal ions
to flow through a fixed bed of retic~ te~l polyurethane foam having ion ~y~h~ngesites to sorb the metal ions.
Throughout this spe~ific~ti-ln and the claims which follow, unless the context
requires otherwise, the word "colll~lise", or variations such as "comprises" or
"comprising", will be understood to imply the incl~lcion of a stated integer or group
of integers but not the exclusion of any other integer or group of integers.
The following ~Y~mples are given to describe typical potential applications
of this new technology. All percentages are by weight except where otherwise
shown.
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PRELIMINARY EXAMPLE 1
A slurry was prepared by distributing 40 parts by weight of ground quartz
particles in 100 parts of water. 80% of the quartz particles were between 100
S micron and 150 micron in size, the re-m~in~ler lay between 45 micron and 100
micron in size. This slurry was pumped both dowl,w~s and also u~w~ds through
a 1.2 metre high block of reti~ll~ted polyurethane foam at particle flow rates in
excess of 1 cm per second with negligible pressure drop across the bed.
PRELIMINARYEXAMPLE 2
A slurry was prepared by distributing 40 parts by weight of a clay mineral in
100 parts of water. 80% of the clay particles passed through a 75 micron sieve.
The slurry was pumped u~w~ds through a 1.2 metre high block of reticnl~tecl
15 polyurethane foam at particle flow rates of up to 1 cm per second. Air was
introduced into the base of the foam bed and rapidly travelled through it in a
vertical direction without s~lhst~nti~l pressure drop.
PRELIMII'I~RY EXAMPLE 3
Brown coal was mixed with water in a high shear mixer to disperse the
fibrous coal particles and to form a slurry cont~ining 30% solids. This slurry was
pumped u~w;llds through a 1.2 metre high block of reti~ll~ted polyurethane foam
cont~ining about 15 cells per linear inch (i.e., 60 cells per 100 mm) at particle flow
25 rates of up to 1 cm per second.
EXAMPLE 1
48.4 grams of a retiç~ ted polyurethane foam cont~ining about 15 cells per
30 linear inch (i.e., 60 cells per 100 mm) was interpenetrated with a llli~Ule of 67
grams of chloromethyl styrene mon-)mer (CMS), 48.5 grams of styrene monomer,
5 grams of divinylben7sn~, 2.5 grams of tohl~n~ and 0.5 grams of
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azobisisobutyronitrile (AIBN) and then cured at 70~C for 24 hours in a nitrogen
atmosphere.
The resultant interpenetrated resin was then further reacted by soaking for
S 12 hours at 55~C in a mixture of l:S by volume of pyridine:acetone.
The foam treated as described above then was placed in a column and a
gold cyanide solution cont~ining 40 percent of quartz to form a slurrywas pumpedupwards through it. A loading of 41,500 mg Au/kg foam onto this modified
10 polymer was obtained. The quartz particles slurry cont~ining the gold cyanide had
the following particle size:
weight %
~ 150 micron 6.8
150-106 micron 57.8
106-75 micron 25.1
75-45 micron 9.2
< 45 micron 1.1
No loss in sorption capacity was observed following the ~ pi~g of the
quartz slurry though ~hic chçmic~lly mn-1ifieci reticlll~tecl polyurethane foam for lS0
hours and no observable building of solid material was recorded.
PRELIMINARY EXAMPLE 4
A gold-con~ining ore (head grade 4.5 ppm) and concictin~ of quartz (29%),
stilprom~l~ne (14%), chlorite (30%), calcite (5%), muscovite (4%), clolomite (3%), r
pyrrhotite (10%), pyrite (2%) and minor minerals tO 100% was ground to give a P80
of 75 micron at a pulp density of 56% and treated with sodium cyanide in a
30 conventional carbon-in-leach plant using a direct injection of o~ygen. An analysis
of the tailings water showed that it cont~in~d 104 ppm of free and WAD cyanide
and 360 ppm thiocyanate. The tailings from this gold recovery circuit were passed
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over a 150 micron vibrated DSM screen to remove any ~ve~ e material and then
allowed to flow under gravity through a column 30 cm diameter and two metres
high cont~ining a 60 cell per 100 mm retic~ te~l polyurethane foam of density 28
kg/m3. No abrasion was observed after 21 days continll~l slurry flow.
EX~MPLE 2
To the tailings pulp described in Prelimin~ry Flr~mple 4 was added on a
molar basis sufficient zinc to convert all free cyanide to the complex zinc cyanide
10 anion. This pulp cont~ining metal cyanides was then passed through retic~ ted and
open-celled flexible polyurethane foams (cont~inin~ either 150 cells per 100 m~n or
60 cells per 100 mm) which had been chemicallymodified to cont~in a~pl~,xi..~t~ly
35% of a pyridine-based interpenetrated polymer. The chemical mo-lifi~ ~tinn wascon~ cted by interpenetrating under nitrogen the reti~-l~tecl polyurethane foam
15 with a solution cont~ining 100 parts vinylbenzyl chloride, 68 parts styrene, 7.5 parts
divinyl benzene, 0.75 parts (AIBN) and 3.7 parts toluene. The interpenetrated
polyurethane foam was cured by heating under nitrogen for 18 hours at 80 ~C in asealed vessel and then for a further period of 18 hours at 80 ~C in air. The polymer
was then immersed for 12 hours at 50~C in a sohltion cont~ining pyridine 20 and
20 ~t~etone 100.
After a 2 mimlte contact with 2.3 g of this polymer in a 16 mm diameter
tube (flowrate 47 ml/min.) the slurry exiting the column was analysed. 98% zinc,83% iron, 87% copper were found to have been removed giving a 95% recovery of
25 WAD cyanide. Once fully loaded with WAD cyanide the polymer was stripped
using a 0.1 molar sulphuric acid soll~tion to generate HCN gas which was bubbledthrough a 1 molar solution of sodium hy~ide to form sodium cyanide.
EXAMPLE 3
An acid mine drainage slurry from a copper mine and co.~t~i..i..g 9.1%
quartz and 11 ppm of soluble copper was passed through the cr-ll-mn described in
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F~mple 2. The coll~mn cont~ine~l a 60 cell per-lOOmm retic~ tecl polyurethane
foam which had been impregnated with di[2-ethylhexyl] phosphoric acid [D2EHPA].
After 1.5 minute contact time, 535'0 of the copper was removed from the slurry.
S EXAMPLE 4
A slurry with a m~imllm particle size of 180 micron and cont~ining 11.9
ppm gold, 11.0 ppm copper, 13.2 ppm zinc, and 14.0 ppm ferric iron all as cyanides,
and 0.3 g/l free cyanide at pH 11.0 was passed through the column as described in
10 Fx~mrle 2 at a flow rate of 90 ml/mimlte. The column was p~ck~ with a 15
cell/inch (60 cells/100 mm) reticulated polyurethane foam which had been
impregnated with a gold-selective organic extractant (Aliquat 336 manufactured by
Henkel Corp.). After a 1 mim-te contact time 63% of the gold cyanide, 1% of the
copper cyanide, 26% of the zinc cyanide and 4% of the iron cyanide was recovered.
15 This example shows the selectivity which can be achieved accol-lhlg to the process
of the present invention.
EXAMPLE S
A slurry cont~ining 10% of solid matter with an average particle size of 100
micron and cont~ining 5.92 ppm of chromillm(VI) at pH 2.2 was passed through thecolllmn as described in F~mple 2 with a flow rate of 90 ml/minllte The cQlllrnn
was packed with a retic~ te~l and open-celled flexible polyurethane foam (60 cells
per 100 mm) which had been rhrmic~lly modified to cQnt~in a~ .x;...~trly 35%
25 of a pyridine-based interpenetrated polymer. The chemical modi~ tion was
con~ cted by interpenetrating under nitrogen the reticlll~te~l polyurethane foamwith a solution cont~ining 100 parts vinylbenzyl chloride, 68 parts styrene, 7.5 parts
divinyl benzene, 0.75 parts azobisisobutyronitrile (AIBN) and 3.7 parts toluene.The interpenetrated polyurethane foam was cured by heating under nitrogen for 1830 hours at 80~C in a sealed vessel and then for a further period of 18 hours at 80~C
in air. The polymer was then immersed for 12 hours at 50~C in a sohltion
cont~ining pyridine 20 and acetone 100.
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After a minute contact time 79% of the chromium (VI) was removed. The
column once fully loaded with chromium (VI), 91% of the chromi~lm was stripped
using seven bed volumes of a solution cont~ining 0.5 molar sodium s~llph~te and 0.1
molar sodium hydroxide.
