Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
W092/22504 210 3 2 4 7 PCT/AU92~00272
TREATMEN? OF WASTE WATER
This invention rela-tes to the treatment of waste water in
order to reduce the level of contaminants therein and to
produce environmenta}ly acceptable products. It is of
particular value in the treatment of acidic mine waste
water.
~.
I In one aspect of:the invention, a multi-step process is
¦-~ : provided including certain steps which are novel per se.
I ~ The process may include for example a multi-step process
Z~ 10 including a first step in which zinc, copper and/or cadmium
~ may be extracted from the mine waste water as saleable
'~: products, while iron and aluminium may be extracted to be
discar~ed as chemically neutral slurries or dried soIids.
~:`` Step 2 may include removal of the remaining heavy elements,
15~ calcium, magnesium and most of the sodium. Step 3 provides
for the removal of~sulphate and chloride, and step 4 may
: prepare~or "polish" the water prior to on-site u5age or
of~-site~;dlscharge. In preferred aspects o~ the invention,
é~c~nomic advantages are maximised by recycle of reagents,~
ao~ ~ whereby~ consumption of~reagents is~si~gni~icantly reduced,
as:well as::by:production of saleable products.
: ~
BACKGROUND OF_THE INVENTION
The~ problems asso~iated with:acidic m~ne waste~water in
terms of water storage, water treatment and usage nd mine
2:~ rehabilitation are~well documented and in this connection
s ':
referlence may be:mad!~elto the detailed papersjand
discussions in the proceedings of:the Xnternational
Symposium Lisboa:90 "Acid Mine Water ~in Pyritic
Environments" ~September 1990)~
i~ ",'~t ~
30 ~ The ubiquitous~generation of acidic base metal mine waste
~ ~ ~ water presents a serious pxoblem in terms of water storage,
l~ : i water treiatment and usage and mine rehabilitation. The
j:: acidic mine water ~AMW) results from the bacterial
,"
!: ~ ca~alysed oxidation of base metal sulphides, particularly
`s "~,
~s~ `
W092/22504 21~ 3 2 4 7 2 - PCT/AU92/0~272
pyrite (iron sulphide). There is no general solution to
the problem of the acid generation, however, there are
: many options to diminish acidic dischaxges especially where
the oxidisable sulphides are located at or near th~
topographical surface (e.g. tailings, dams and dumps, waste
-,; rock dumps and shallow mine workings and open pits). The~e
" ., .
t~chniques include barrier methods that isolate the
sulphides (mainly pyrite) fxom oxygen or oxygen containing
water, and the use o~ chemical additi~s to inhibit the
grow~h or development of iron-oxidising bacteria. Recent
procedures have included the incorporation of large amounts
of alkalinity and/or phosphate within the sulphid~s, the
~ use of surface geophysics to identify potential problem
: areas, the sealing of fractured stream beds using polythene
~ 15 or si.licate based grout and the use of anionic sur~actants:: ~ and bacteriocides to lnhibit the activity of iron oxidising
bacteria. These conventional methods have all attempted to
. minimise the formation of the acidic mine water but are
: sub~ect to p~sible failure due to the vagarie~ of nature
; 20 with potentially ~ dangerouR results .
~, ~
The approach detailed below aims~o treat the acidic mine
water, once formed, in a chemically efficient and cost
e~ffective manner:to produce high quality dischargeable
~ater~and marke~able~extracted bas~e metals and:salts ln an
envlronmentally:acceptable package.
: PRIOR ~RT ~ :
; US patent 4,652,~381 d~scloses a process of treating
industriaI waste water contamlnated wi~h environmentally
unacceptable amounts of sulfuric acid and heavy metals such
as lead, copper or zinc which permits lowering of the
concentration of the contaminants to a level:~pexmitting
discharge *o the ~ewer. The water to~be treated is
directed to a first reaction and settling vessel where
: calcium carbonate is added along with an oxidation medium
such as air which also functions to stir the stored waste
:i : watex, Suficient calcium carbonate is added to bring the
1.,,,
!~
~ ,,
~la3~l7
W0~2/22504 _ 3 PCT/A~92/00272
pH of the solution to a level of about 5 and at the same
time react with the heavy metals pxesent such as lead,
copper or zinc. Calcium sulfate and respectivP heavy metal
~! carbonates precipitate and settle to the bottom of the
i 5 treatment zone where they may be readi]y remov~d. In a
second treatment v~ssel, calcium hydroxide along with
enough calcium carbonate to maintain an excess of carbonate
ion are added to complete separation of the heavy metals.
Final removal o~ precipitate ~rom the solution is
accomplished through a suitable filter.
,
..
: US patent 5,0}3,453 discloses a method which can be used to
remove dissolved heavy metals and/or iron ~rom nearly any
: aqueous stream. The invention is particularly useful in
removing the large concentrations of copper, nickel, zinc,
gold, silver, cadmium, tin, chromium and lead ~rom pickling
acid wastes and other~acidic waste streams formed in the
;metal~finishing industr~ies. In the method of the
invention,: a~selected:carrier precip~itate is created within :~
an aqueous wast:e~solution which:is contaminated with heavy
20~ mèta~ls~andtor iron. ~ The contaminants are thereby caused to
coprecipitate with~the carrier precipitate and are thus
;r;emoved`~rom the~aqueous solution. ;:
JP 80049555~di~-closes~treatment~:of waste~water containing
:heavy metals and~:organic~matter involving~biological :
25~ oxidation to~decompose~the:organic~:matter. ~Heavy metals::
are~conv,~rted to~their carbonates:and the pH is
subsequently ra~ised~:to precipitate heavy metal:hydroxides,
the pre~ipitate~al~so containing heavy meta:l carbonates.
In ~P~59203692t~waste:water from pulp~production is
30~ oxidised and tr~eated with calcium:carbonate:and a high
molecular weig~t organic flocculant. ~ ; :
: ~
. ~ US~paten~ 3,725~,266 discloses a process for removing one or
~: ~ more metal compound contaminants f~om con~aminated
` : industrial waste water comprising precipi~ating the metal
. ~` 35 : compound contaminants from the waste water to form an
,, :~
~i, '
21~32~7
W092f22~04 : _ 4 PCT/AU92/00272
aqueous metal compound sludge, allowing the sludge to
settle, concentrating the sludge by centrifugation and
reclaiming the metal compound contaminants from the sludge
for reuse as either the metal compounds or the free metals.
The preferred precipitating agents as hydroxides and
¦ carbonates, such as, sodium hydroxide, calcium hydroxide
and sodium carb~nat , which produce the lnsoluble metal
hydroxides and carbonates, respectively.
Prevention and~or control of acidic mine water (AMW)
~ormation depends upon an understanding of the chemical,
biological and geological characteristics of base metal
sulphides. A series of chemical reactions (given below)
describe AMW formation which results from the exposure and
weathering o~ pyritic material (FeS2) normally present in
jbase~ metal mine~and coal wastes to t~e combined e~fects of
atmospheric oxy~en, water and iron and sulphur oxidising
bacteria such as
Thiobacillus ferrooxida~ns (T. ferrooxidans~, -
20 ~Ferrobacillus ferrooxidans ~F. ferrooxidanS? and
Thiobacillus thiooxidans (T.:thiooxidansl.
2FeS2 ~+ 70~ ~ 2H~0 =~2Fe2+ + 4so42- +4H+
Fe2+ ~+ ~l~/2~0~ ~+ 2H+ =: Fe3+ : +~ ;;H 0 ~ (2)
: (bacterial assistance)
:: 25~ Fe3~ ~3H20:i~ Fe(OH)3(s) + 3H+ ~ (3)
. The~ stoichipme!try,of equation,(l) shows that one mole of
FeS2 produces:two moles of acid ~H+).~ In turn :~e2~
: generated by reaction (1~ is oxidlsed into~ Fe3+ and
produces an additional three moles of acid (equation 3).
30 The net resu~lt; is that for every mGle of pyrite oxidized,
j : four eqlli~alents of acid (H~) are produced.
. I
~j ~ As the pH in the immediate vicinity of the pyrite falls to
5:~: less than 3, the increased solubility of iron and the
W092/22504 2 1 ~ ~ 217 PCT/AU92/00272
decreased rate of Fe(OH) precipitation affects the overall
rate of acid product.ion. At this point, ferrous iron is
oxidised by T ferrooxidans and the ferric iron in turn
oxidizes the pyrite :
FeS2 ~ 14 Fe3+ ~ 8 H2O = 15 Fe2~ + 2S042- ~ 16H-+~ (4)
, .
The rate of acid production is high and is limi~ed by the
conc~ntration of ferric ions. Fe3+ activity beccmes
significant ak~a pH of approximately ~.5; a ~icious cycle
~: of pyrite oxidation and bacterial oxidation of Fe2+ resul~s
: 10 from the combined e~fects of reactions ~ and 4. The rate
of reaction 2 exerts prlmar~ control on the cyclP by
Iimiting the availabi:lity of Fe3+ which is the ma~or ,
; oxidant of pyrite.
The ~presence of the acidic environment:together with the~
~oxidised Fe (and~probably Mn) readily:~attacks other base
met~al sulphides present allowing the:dissolution o~ Cu, Zn,
Cd,~ Co and Ni and~other trace metals present in the
sulphi:des ~e.g. Mo,~ Sn,:Ag, Hg, Sb, Bi). The high sulphate
: levels~will result in Pb being precipitated as an insoluble
20 ~sulphàte following the decomposition of Pb ore ~galena).
Some~occlusion of:~Ag~in` the Pb sulphate will probably~:occur
:`and~les~s soluble~basic salts~of~other~metals may also : ~ :
precipitate (e.g.~ Sn,: Moj. The produ~cts o~ ~oxidation of :
the;~llsted metal su~lphi~de~ores by:~T~.; ferrooxidans are shown
:25 in the~following:~table~
~ - :
,~ g ~
~, ~
: ' !
~ :~ : :
''''~
~ '
.
.r,~,~
WO ~2/22504 2 10 3 2 4 7 - 6 - PCl /AUg2/00272
METAL SULPHIDE ORES OXIDISED BY T FERROOXIDANS
~L~ Formula Soluble Ions
Arsenopyrite Fe S2 Fe As2 Fe, some As
at very low pH
values
.~ 5
Bornite CuS Fe S4 Cu Fe
Chalcocite Cu2 S Cu
Chal~::opyrite Cu Fe S2 Cu Fe
Covellite Cu S Cu
Enarglte 3 Cu2S As2 Ss C:u (As)
Pb S Insoluble
Galena
su lphate
Marcasite Fe S2 Fe
Millerite Mi S Ni
:: ~ ;: 15 Molybdenite MoZ2 Mc~
; Orpiment `: As2S3 (As)
P~rri~e ~ ~ F~ S2 Fe
:
Sphalerite ~ Zn S Zn
Tetrahedrite ~ Cu8 Sb~ S7 ; Cu ( Sb)
'
~ S
:
:~ ~ ~ - :
,
~: :
', , ' ~ .
~',''J
~'
21~3247
W092/22504 _ 7 PCT/AU92/00272
Further appreciation of the nature of the problem may be
gained by comparison of a waste water composition set out
i in the following Table 1, with the impurity levels allowed
by the New South Wales (Australia) State Pollution Control
~ 5 Commission 5SPCC) for Sche~ule 2 Discharge Water together
.. f with U.S. Drinking Water Standard Requirements in Table ~.
The data in Table 1 are from Woodlawn Mine, Tarago, N.S.W~
~ustralia.
.'.
~,
. ~
:
- ,
.
:: :
~ , ;
: ,
,
'
'.
,, :
, ,,~,.,
~6~
WO 92/22504 210 3 ~ 4 7 PCr/AU92~00272
~ WASTE WATER COMPOSITION (ppmL
,
.: "
.. " ~ North Dam South Dam I~3~x
~, or. ion Water Water ~
. "~ ~ .
Cu 100 77 41
,~ 5 Pb 1. 5 lo4 f).2
~ Zn 3000 1860 737
~1 Fe 200 92 41
-, Cd ~ I2 ~ ~ 9. 3 5 . 0
Mn 130 84 31
Na : 300 370 82 ..
K 3 2
Al 610 ` 355 170
., ;~ Ca ~ 400 ;: 390 : 140 '
Mg ~ 1700 ~: ~ 920 ~ 330 ;-
15 ~ 5~0 ~ 1690~0~ 9~20 : 3880 ~ :
CI ~ : 200~ : 12:0 ~ ~ : 550
pH: ~ : 3 . ~ :3 . 2:: :: : ~ :3 . 3
~ ~" '
~ : :
WO 92/22504 9 210 3 2 ~ 7 PCI /AU92/00272
_. :
,'~
TABLE 2. WP~ER O~ALITY ~3T}~NDARDS
.~ :
1.
., ,
,~
' Paramoter ~PCC 9ch-2. (ppm) 8 EP~ Drinkinqt : watex (ppm) i.
:
. :
: 5 As I~I L 0. OS
A s V
Ba ~ 1. 0
B e ~ 0 0 1 ~ 0 0 1
10~ Cr; I I I ~ : 0 . 05
, ~ Cr ~IV
15:~ :: Pb -~ 0. 05 : : o 05
Mn ~ O . OS ~ 0 . 00~ :
D~ ~ N 2 ~ 0
S 0 4; ~ 2 5 0
C~ 250~ ~ ~
`pH ~ 6. 8 ~; 8 .~5 ~ 5 -i 9
:::: ~ ~: : ~ : : :
~ : ~
"
: ^ co~al CtJ - present ~s complex ion ~.cj. Wlt~ ', C~J, t~
~.
~ ,
21~32~7
WV 92/22504 10 PCl`/AU9 /0a272
DEVELOPMENTAL EXPERIMENTATION
~.
Experimental measurements showed that good cation and anion
removal from the Woodlawn AMW could be achieved using i~n
exchange techniques but capital costs and reagent costs
were high for a purification plant operating solely on ion
exchange (IX) processes. Likewise Reverse Osmosis (RO) or
Electrodialysis (EDR) is capable of providing high quality
¦ water when used as a stand-alone technique but is
inefficient in the presence of high levels of dissclved -:.
solids and membrane fouling may occur due to gypsum (CaSO4)
precipitation or the presence of organic contamin~nts.
: Both these techniques (RO and EDR) and probably IX are
ideal for "final polishing" of the water prior to discharge
but a relatively cheap and e~fici~nt chemical pretr~atment
15 operation is required to remove the bulk of the dissolv~d :~-
solids to decrease the operational cost of IX, RO or EDR. ;~
, ..
De~el~opment of the process of ~he invention evolved through
several stages employing various techniquesl as follows.
Ion~exchange processes
~Cation and anion lon exchangers were used to investigate
: the removal of:soluble ions from the Woodlawn AMW. The
cation ion exchanger~removed all cations other than t he
: alkali metals~(sodium:and potasslum) very eff:iciently.: The
capacity for:the;alkali:metals was low but was proba~ly
accept~able and the:AMW could be ~ed directly to ~the resin.
Regeneration wa~s~ achieved with hydrochloric acid followed
~`~ by conversion to the sulphate form for use.
:. : : ~
~ The r moval of sulphate was more difficult and both strong
,~
- and weak base`~anion exchany rs were used. Again stripping
j ~30 and regeneration was achieved.
¦ The overall costing for a large AMW treatment plant was
uneconomic in terms of both capital costs and the
~ regeneration reagent costs. A further disadvantage was the
..
~.
.
21~3~7
W092/2250~ PCT/AU92/0027~
inability to handle organic non-ionic contamination and the
difficul~y of obtaining elemental separations without very
careful reagent elution control.
.', '
~¦ 2. Chemical precipitation with RO and sodium sulphate
crystallisation.
, A series of experiments were carried out aiming at
i producing a zinc carbonate/zinc hydroxy carbonate
~ precipitate directly from the Woodlawn ~MW. A stepwise
. .
addition process was developed using a range of pH
adjusting chemicals to change the pH of the AMW such tha~
the precipitation of the component cations occurred in a
controlled manner. Neutralisation was carried out
successively with CaCO3 in stage 1 to a pH about 5, and a
.li residue separa;ted containing Fe and Al. In stage 2,
treatment with Na,CO3 raised the pH to 8 to 8.2, and a
residue separa~ed containing Zn as a basic carbonate, as
well as Cu, Cd, Co and Ni. In stage 3, lime was added to
increa~se t~e pH to 10 to 10.5 to precipitate Mg and Mn, and
in stage 4 NaOH~was added t`o increase~the pH to 11 to 12,
; 20 thus precipltat~ing Ca and more Mn. After pH adjustment
with sulphuric acid, the liquid phase product of stage 4
, . . ~ -
was treated by reverse osmosis to produce high quality
clean discharge water and the concentrate was crystallised
to produce~a marketable sodium sulphate. Other products
were zinc carbonate, zinc oxide and zinc metal and a Cu,
;Cd,~Co, Ni fraction which was readl~ly cGnverted to a cu
cementate.
~: , ::
i Extensive testing showed the process t~ be technically
viable but expensive.
3. ~Chemical precipitation with RO~`~
~,............. ~.
,.,.. ,
, ~ .
The process is similar to 2. (above) but the concentrate
-~ ~ from the RO is directed to an evaporation dam. The cost is
,.~.
, ,j
,,
"~,s s~,
'~ ~
W092/2250~ 210 3 2 4 i - 12 ~ PCT/AU92tO0272
reduced, but with a potential rehabilitation problem
occuring in terms of th~ long term operation of the ;
evaporation dam. ~-
4. Chemical precipitation with an evaporator ~,
This process replaced the RO with a vapour recompression
evaporator and the residue again was directed to an
evaporation dam.~ The cost was slightly lower than 3.
(above) but with the same long term rehabilitation problems .~
with the dam~ ~:
,."~
10 Further Proc~ss DeveloPment .. :
,;' ' . '
A re~iew of the ~MW technology showed that although
discharge quality water could be produced using the ~:
~ombination of pH ad~ustment/precipitation and RO, EDR or .
; Evaporators, there~we~e a number of problem areas. These
15~ were~
Cost of treatment~- both capltal and~running~costs were
oo:high.
~:
2. ~Increasing;leve~ls~of calcium and~ sodl~um.
The slow: but ~continuous precipitation of ;gypsum
: (CaS04~ on membrane and~evaporator surfaces causes a
rapid loss of per~ormance. ~
Sodium salts are::very soluble~:and are~expensive to
crystallise~
3. High reagen~ consumption
: 2~5 - - The addition of pH or Eh adjusting reag~nts to ~ :
:~ . change the acidity or alkalinity~of the total volume
:~ : of water~is often an inefficient way of removlng .j.
mlnor components. .:
4~ Potential build up of problem contaminants ;;~
- The progressive build up of; magnesium (difficult to `.
: ~ precipitate a~ a pH of less than 10 ~ 11) and
,`.
2~32~
W092/22504 - 13 - PCT/AU~2/00272
.
manganese (difficult to precipitate quantitatively ~ ;
with pH adjustment alone) causes purity problems in
the proposed sodium sulphate product. ~ ;
5. Slow processing speeds
S - The use of settling tanks or thickeners and bulk
filtration are o~ten slow processQs if ~he svlids
are bulky or gelatinous. Hydroxides in particular
are often slow to filter.
' ,~ '
6. Contamination from particulate or organic components
- A pretreatment filtration or settling system may be
required~ ~
A cost effective study of the AMW purification process
showe`d that the first two stages were justified in terms of -
~ ~ fficiency and peformance.
15~ e.g. Stage 1
.
AMW (pH 2.5 - 3.3) is treated with crushed limestone in
an agi~ated tan~. ~ slight excess~of limestone is
required.~ The pH of the water rises to 4.9 - 5.0 and
re~ults i;n the precipitation of 90 ~ 95% of the Al and ;~
Fe. Oxidising conditions are mainta1ned using air
; ~ sparging. Th~is precipitate se~tles quickly and~ can be
removed by thickening~, it also acts as a feed water -~
particulate~removal stage with~a signi~icant reduction
in organic content due to adsorption on the bul~y~FelAl
~,.
-5~ hydroxides.
S~age 2.
- ~ . . .
Th partially neutralised ~ater from Stage l. (pH 4.9 -
5.0) is then ~reated with sodium carbonate (Na?CO3) in
an agitated tank. The pH of the water rises to 8.0 to
8.Z and results in the precipitation of Zn, Cu, Co, Ni
an~ Cd and the remaining Al and Fe. The precipitate is ~;
. . ,
processed ~o produce marketable products. Zn is ~`
W092/22504 210 3 ~ 4 7 - 14 - PCT/AU92/00272 ~ ~:
converted to zinc oxide or zinc metal and Cu is :,
produced as a cementate containing the Co, Ni and Cd. -
The Al from stage 1. together with Al from the Stage 2. ~:
precipitate can be extracted to market a chemically -
. purified ~l product such as aluminium sulphate.
The following stages using pH adjustment over a wide range
(to remove Ca and Mg) and expensive plant tRO., EDR, -~
Evaporators) were reviewed and further development showed .~ ;-
the possibility of a more effective technology based on: :
fatty acid derivative chemistry, as well as a further more
effective technology based on the use of organic bases to
remove soluble anions.
",~;
THE APPLICATION OF FP,TTY ACIDS TO THE TREATMENT OF ACIDIC
MINE WASTE WATER
Following the cost effective removal of Fe, AI, Zn and Cu
: from the acid mine water by the stepwise p~ adjustment :
:using limest~one~and~sodium carbonate, a novel approach to
: ~ the removal of other cations has been developed. Long
chain fatty acids are~well known for:their formation of
20 : in:soluble precipitates with Ca and Mg ~(e.g. use of soap in ~-
. .
~ hard water). Experimental work at Woodlawn Mine on AMW has ~ ~ -
:: : demonstrated that Oleic (Cl8H34O2) and Stearic
: (Cl8H36O2) acids effectively precipitate Ca, Mg plus other
heavy metals from the:partially~ treated Woodlawn waste
water. These C-18 acids were most conveniently added as
their soluble Na salts and were shown to be more efficient ;~-~
for cation remoYal ~kan the shorter chain length ~SR~C
reagents. . --~
: ' :, ; ~'.' :,'
. . ~
: -...,~;.....
"
`'~
.''''''.'''''
':': ':
2~ 032~7
W042/2250q - 15 PC~/AU92/00272
ppm Cu Zn Fe Mn Ca Mg Al Cd SO ~ ,
~eed Water <0.1 2.5 <0.1 32 495 600 0.24 .16 ~440 ~:
pH 8.3
After Oleic ~.01 0.15 <.01 0.01 23 55 0.05 <.01 9240 :~
5 Treatment .. ~.
After ~.01 0.02 <.01 0.0~ 5 ~5 ~.01 <.01 9100 :.
Stearic
Treatment
", .
Conditions 5 gms Fatty Acid as Na salt to 11 L -
10 pH 8.3 Feed Water stirred in flotation cell for 20 :~
mins. Temperature used = 20-22C~
' ~ "
The me~al fatty acid salts can be removed by filtration or
flotation and on acidification (pH1-2) wit~h hydrochloric
~acid the:fatty acids are regenerated and the cations .
15~ solubilised for treatment as a concentrated solution.
me removal of Na lS also observed but the efficie~cy of ;~ "~
: alkali metal removal is very:dependant on fatty acid
composition and temperature. : :~
- .
~The use of the fatty acids allowed the simple removal of Ca
and Mg and also reduced the remaining heavy metals to
levels suitable ~or discharge. Also the ~application of .
:ultra filtration (UF) and micro~iltration (MF) techniques
using ceramiC fijlter,s,or filter pads~ lS promisin~ for the ;, ~ .
rapid, continuous and efficient removal of the fatty acid :.
`meta~ salts~
THE USE OF ORGA~IC BASES TO REMOVE SOLUBLE IONS FROM ACID ;~
MINE WATER .;
,. . ~ :,
~xtensive research and development has demonstrated the ..
ability to remove the cations from AMW in a cost effective
30 manner. Howevser, prior to the present invention, the . ~;
,,,~.,
W092/22504 '~ 4 t PCT/AU92/00272
removai of the corresponding anions (essentially sulphate,
phosphate and chloride) has only been achieved by
crystallising sodium salts which is expensive in terms of
both capital and running costs. We have now developed an ~;:
alternative approach using organic bases, such as
nitrogen-containing fatty acid derivatives, to form
insoluble or partially soluble salts or sulphate micelles
which can be removed from the AMW.
,~,
Organic bases such as amines (jprimary, second~ry and
io tertiary), ~imides, diamines and quaternary ammonium
compounds can form insoluble or partially soluble salts
with sulphate anions in acidic aqueous solutions. Chloride
salt~ formed with the organic bases tend to be more soluble
but some co-removal of chloride with the sulphate
lS precipitates is ofken observed.
The ~ollowing considerations need to be taken into account
~ i
for anion precipitation:
(a) The solubility of sulphate or chloride salts or
compounds in acid mine water or processed feed
~ solutions and the effect of other cations or anions.
. ,;
) The composltion of the feed water e.g. ~H, Eh, ionic ~:
content, organic content.
(c) Feed water temperature - all sulphate and chloride
salts appear to be much more soluble in hot water ~-
.. .., 1, '~,:,
(d) The ability to recycle the reagents e.g. treat anion
-precipitate wi~:h Na~CO3/NaOH at pH 10-11 to reform
the amine. ~ - `
(e) The use of other reagents to bring about the hydrogen ~; `
substitution to reform the amine and release the ~ -
anion as an acid. `~
;;" ~""~'
, - ~
2 ~ ~ ~s~ r~ :
WO 92/22$0'1 ~ 17 - PCl`/Al~92/0027 !
(f) The availability of a water soluble (pH 6-8) reagent ~,
which precipitates sulphates would have a distinct
advantage in terms of removing anions after the ~",
:,
cation precipitation stages. Possibly ~he formation '~
of sulphate micelles can be considered e.g. with ;'
amine oxides and surfactants.
;,:, ,;
(g) For ease of reagent handling amine gel formation must
be a~oided. ''
,
Anion Precipitation Experiments ~ ~
.
Bench scale experiments were carried out using ~rucine,
~benzidine and dodecylamine. ' ,
(a) To precipitate sulphate from dilute hydrochl'oric acid
- only benzidene was successful, however, this is an
established analyt~ical procedure; the use of ;~
. ,~ .
15 ~ benz.idine is not to be recommended, from a safety ",;'
"
viewpolnt. ~ ,, "
~(b~ Experlments,on Woodlawn ~ pH 3.1, SOZ~ 9500ppm, ,''';''
Cl- 120ppm.~Note- SPCC discharge limits are: , ,
04-- ~ less than 250ppm ~,~',,;
~ ~ Cl' less than 250ppm ~ ',- '~',(,
Procedure;~- The reagent was disper'sedjdissolved in ','',~'
warm dilute hydrochloric acid ~(2%~v/v) and ~ ,;,,';-'',
approximately lOgms of each amine~were added with ~
, , stirrin,g to~ ,of,~AMW. ~The pr~eclpitate was, all,owed '',~'''`~.'
to settle and was removed by decantation and ~,,''; ',";,~
filtration,,~ The filtra~e was assayed for sulphate.
The precipitate obtained from the AMW was brown (nGt `
white ~s expected for a pure amine sulphate) which '~
indi~,ated the coprecipitation of other species with ''',-~ ,
3V the sulphate. `~''''
, ~
W092/22504 2 1~ 3 2 4 7 - 18 - PCT/AU92/00272
Results: ~;
'.,.' :~: ,, :,
Run No. NDW 1 NDW 1 NDW 3
Temperature 40C 25C 2ZC
Rea~tion Time 10 mins 10 rins 30 mins
5 S042- levels in ppm
. ,~ ~ ' '.
Benzidine 120 50 30
Brucine 300 200 lO0
Dodecylamine 350 ~00 100 ~
' :
After filtration the ~precipitate was treated with
Na,C03/NaOH at pH 10-11 to recover the amine and to
~solublise the anions. Recoverles of 85-90~ were obtained.
The precipitation of sulphate from Woodlawn Acid Mine Water
(WAMW)~feed (pH~3.1) with amines has prom~ise but in
~practlce the~addition~of the amine as a soluble chloride
;~ 15 ~vould result~ln~exch~Dging sulphate~ions for chloride ions.
To;investigate the removal of chloride, the reagents were
dlspersed ~in di~lute~ormic acid (1%~v/v~j~and this resulted~
; ~ in~a~reduction~of chloride ion content with~ brucine and~
; dod:cyiamine~(~rrom 120 ppm to 80 ppm).~
20;~The removal of;anions by precipitation~as~descrlbed above ~ ~ ;
can be~applied~;to~t~h~e AMW feed directly,~however it lS best ~ `~
applied following the removaI of cations with fatty a~id
salts, which i~s dl,squssed ln!more detai~l below.
Further- ~xPeriments~on~sulphate Removal~
25 Test solutions were~prepared from ml~Xtures of Sulphuric~;
Ac}d, Sodium Sulphate and Sodium Hydroxide to give a 3,000
ppm and io,ooo ppm sulphate solution at pH values of 3, 5, `~
7 and 8.
, - , ;~
.
;,~, ,
W092/22504 2 ~ 3 3 ~ 4 7 PCT/~92/0027~ :
A temperature of 30C was maintained during the .
experiments.
The surf~ctants used were -
Sodium lauryl sulphate ~SLS)
Alkyl benzene sulphonate (ABS)
Ligoin sulphonate (LS)
Dodecylamine (in about 2% solution) was dispersed in
1% (v/v) HCl and addecl in slight excess to the sulphate
test solutions. These were then stirred ~or 30 minutes. ~ ;
the dispersions were treated with 0.2 ml 0.1~ surfa~tant
and stirred for a further 2 minutes. . :.
Solid/liq~id separation was achieved using a~ 0.45 micron ; ;
micro filtration assembly.
: : ,,.,' :,
~ Results ;
15 ~ Feed-3,000:ppm Sulphate Solution:
: Filtrate SO~ content (ppm) .-.
YE~E~n~ SLS ABS ;LS~
pH of f~eed solution
3 ;550 300 160 ~ ; ;;
~350~ 200 200 .;~,
7 150 ~00 150 :
,. " , .~.~ .
250 450 450
,',', :'~,'
~Fe~d-~10,000 ppm~Sulphate S~olution
Filtrate S0~ content (~ppm)
25 Surfact-nt ~ SLS ABS : LS
pH of feed solution
3 ~00 250 150
300 200 200
7 100 300 1~0 .
8 250 500 400
~'".
",~,.....
W092/22504 21~ 3 2 4 7 - 20 - PCT/AU9~/0027
The maximum permitted discharge levels for sulphate is 250 ;
ppm. The results obtained indicate that low sulphate
levels can be achieved in aqueous e~fluents (below 250 ppm)
using the technique of surfactant induced micelle formation
with separation by micro-filtration following the formation
of sparingly ~olub~e amine sulphate salts. ~ ,
The~ld953~a~ of_~reated Water
~,
Local EPA requirements usual1y define water quality
characteristics which must be achieved prior to discharge.
1~ Practical approaches have included RO, EDX and ; -
Evaporation as final stage purifiers or "water polishing" ~,
techniques. However these processes are expensive to
install and run and the use of "biobed'l systems ls ,,;~;,
preferred. ,~, ~
1~5~ The "biobed" system uses living ~iolog1cal~systems to ,,,,',
absorb the remaining heavy metal pollutants. The water is , ,;,
allowed~to pass~through~a series of weir s~tructures~, ,,,,~,,~,
c~nstruc;ted to~al~10w adequate contact with the biological ,,~,
absorbers. Systems using bacteria, alyae, moss and simp~le ~ -"
20 p1ants~,have been~used~wlth considerable success, ~ ,
Another technique utilises the percolati3n of water through
columns of min~eral absorbers such as marble ch1ps, clays or
zeolites and soi~l~s. These materi;a~ls act~ in both an ~
absorptlon and~;ion exchange capac1ty as we11~as fi1tering
out any remaining particulate matter~
THE INTEGRATED PROCESS
A preferred embodiment~ of this invent;i~n l5 111ustrated in
the accompanying Figure~1, wherein~
Acid mine water A,~ at a pH of 2.5 to 3.3, is treated with
crushed limes~one 1.1 in an agitated tank 1. The pH of the
' ~;
W092/22~4 2 i ~ 3 2 ~ 7 Pcr/Au92/oo272
water rises to 5.0 and results in the precipitation of 90
to 95% of the Al and Fe. Oxidising conditions are
maintained using air sparging.
The pro~uct of this stage is separated into a solid phase ~"
1O2 and a liquid phase 1.3. The solid phase containing the ~ ;
Al, Fe residue is removed at 1.4.
. ' '';':',''~ '"'"
The partially neutraliz~d water.from stage 1 (liquid phase)
at pH about 5 is then treated with Na2CO3 2~1 in an
agitated tank 2. The pH of the water rises to 8 to 8.2 and
resu~ts in the precipitation of Zn, Cu, Co, Ni, Cd and the
remaining Al and Fe~ The product of this stage is
.. ...
separated into a solid phase 2.2 and a liquid phase 2.3.
The precipitate (solid phase) is treated via 2.~ to remove
~ for marketing Zn~as metal and/or oxide and~Cu with Co, Ni,
Cd as a cementate. It~may also be possible~to extract the
Al ~and market a chemically purified Al product. `In stage
3, s41uble fatty~acid salts 3.1 are added to the tre~ted
water 2.3 at pH 8 to 8.3 to precipitate Ca, Mg, Mn, som~ of
~the Na and to scavenge the remaining heavy metals. The
20 ~ precipitate 3.2 is r~emoved either by flotation or filtering
~; ;via~3.4 and trea-ted~to~recover the fa~tty~acids for -
- r cycling, and t~le Ca,~Mg, ~n for market;in~ as~ chemically
pur~ified salts~'ë~.g.~ CaCO3, CaSO4, CaF~, Mg5O4, MgF~, MgO,~ A,,
MnO2) as described in more~detail below.
~ The liquid phase 3.~3 lS treated in stage 4~with fatty acid
~amines 4.1 t~ ~rec~p1tate the anionsj sulphate and
chloride. The aromatic amines are relatively stable and
can also be ~ecycled. The product~o~ stage~4 is~separated
into a solid~phase 4.2 and a liquid phase 4.3 by
30~ ultra-microfi~ltration.
~emo~ed amine sulphate 4.4 is subj~cted to alkali treatment - `
in 4.5 ~o separate the amine, with productlon of sulphate -
~salts or sulphuric acid removed via 4.8. -
, ': `". ~.
W092/22~04 2 1 0 3 2 4 7 - 22 - PCT/AU92/00272
The amine is purified in 4.6 and solubilized in 4.7 and
recycled to ~
Only minor "polishing" of the liquid phase 4.3 is required.
A reverse osmosis (RO) stage was originally contemplated a~
a final "polishing" step prior to discharge, however, it is
believed that in most cases this will not be necessary to
meet the SPCC Schedule 2 specifications.
An algal/p~ant "biobed" system 5 or a marble/clay column is
now preferred as the final stage, because only minor
"polishing" is required. Clean water is discharged via 5.1
and an algal-plant residue removed at 5.2. ~ -~
The solid phase 3.2 recovered from ctage 3 via 3.4 contains ~.'., ":$
Ca, Mg, Mn, (Na)~ and traces of other heavy metals as fatty
acid~salts, and is ~reated i~n the following manner~ The
15 ~ s~id solid phase~is~acidified in 3.5, producing a solution
o~ catlons in~ acld 3.6, from which products 3.7 are
obtained, compr~ising MgSO4, MgO, MgF~, CaSO4, CaCO3, ~aF~
The ~atty acids~separated from 3.5~are subjected ts ~ ;
sa~ponication in~3.~to produce sodium fa~ty~acid salts 3.9 -
: 20 ~ ~ whiah are recycl~ed~to 3.
The success of~this treatment is illustrated by the process `
~liquor composit~ion~set~out in the following~table~3. ~ -
:
. ~ ~
,'-:
: ~ ' ~ ,':'~
.:; .:
W092/2~50~ 2210 3 ~ 4 7 PCTJAU~2/00272
TABLE 3. .~. .
PROCESS LIOUOR COMPOSITION (PPM~ REFER FIG. 1) ; i~
LIOUOR FROM ;;~
ELEMENT 1 2 3 4 5
Zn 3000 50 0.3 <0.1 <0.1 . :~ .
Fe 10 0.1 0.1 <0.1 ~0.1 ~ :-
Cu gO 0.1 0.1 ~0.. ~ <0.1 ';'"~.'""';,.,":'
,",
~1 50: 0.1 0.1 ~0.1 : <0.1 ;~
Cd 12 1 0.1 <0.1 ~0.1 .
: 10 Co 7 1 0.1 <0.1 c0.1
Ni 11 1 ~ 0.1 <0.1 :<0.1 ~; "
Ca 600 500 20 10 10 `;`
Mn 130 50 1 ~0.~ <0.1 ~ .. ~,.
Mg 1750 ~1750 20 10 10
15~ ~ Na ~ ~ 300: ~ 270;0 800 400 400
SO ~ 14000~ 14000; 12700 250 200 .
ci~ 200 ~: 20Q 200 20b 200
APPLI~CATIO TO OTHER:FIELDS OF T~HE ACID MINE WATER
TREA~TMENT TECHNO~OGY :~
Z~0 ~ Th~ process of~the~presênt invention~can~be applied to~a
wide range of waste;~waters, .in additlon~to acid mlne wastè
The process of the~present invention~utilizing the stepWlse ~ :
rèmoval of components~from the waste water is a:flexible .~
25 approach which ca~;be applied to a widè range of waste ~ x
waters. :Other~:waters~derived from the mining lndustry are .~.
:: obvious~areas of application but~potential~exists in other :~
industries for a cost~effective procedure~which~produces
~ high gu~ality discharge water and marketable:products which
: : 30 were previously thought to ~e waste materials. Also in
: ~ m~ny cases the quality of plant or agrlcultural feed water ::~
is inadequate and po~ential exists for water puriflcation.
~ ' :
W092/22504 . pcr/Aus2too272 ~ ~
21032 47 24 ~
Malor Industria1 Users of Water
Pu1ping and paper making
Stee1 production
Power generation
Alumina refining
Meat industry
Coal washing : .
Dairy industry .
Coal to oil conversivn .
10 ~ Potato processing
Iron ore mining and benefication ;~
Food canning~
~ Brewing ~
: ~ Wool yarn production
; Wool securing
; Petroleum r~e~fining
Extractive~metallurgical in~ustries
" , "
Malor~Industrial~Producers~of Aaueous:Eff1uents ~ i
Textile~ ndustry~
20~ P1~stic:Mate~ia1s~:and~Synthetics
: Ph~armaceu;ticals~
Paint~and Coatings~
Org~anic Chemi~ca1s~and Pestici;des
25::~Pe~roleum Re~f:~ln~lng~
Rubber Product~s~
:`: Leather Tannl~g~ an~:Finishing~
Ore~upgradLng:;and~metal smelting
IElectrc3pllat.Lng,fand~metali,finishing
30: Electronic c~omponents
St~orage~and~Primary~Batte~les~
Machinery~and~Instrument Manufactu:r~e~
It will~-be clea~ly understood that the invention in its : : ~.
general ~aspects is~not 1imited to the specific:details . ;
35 rf~erred to hereinabove. : ;~.
,
'.~;:
;. ~, .,
