research inpressure leachingt - saimm · 642 journal ofthe south african institute ofmining and...

632 Journal of the South African Institute of Mining and Metallurgy July, 1969

RESEARCH IN PRESSURE LEACHINGt

Franz E. Pawlek*, Dr.-Ing. (Visitor)

SYNOPSIS

This is a summary of investigations in the field of pressure leaching carried out at the Institutefor Extractive Metallurgy of the Technical University of Berlin-West during the last seven years.The efficient dispersion of gas in a liquid and its dissolutions as well as the events at the phaseboundary when leaching ZnS are reported. At the end two examples are given for the use of pressureleaching in the processing of smelter by-products.

INTRODUCTION

About 20 years ago, experiments were independently started in Canada and inBerlin on the subject of dissolving sulfidic ores without preliminary treatment bymeans of leaching under increased oxygen pressure. In Canada ammoniacal solutionswere mainly employed, and F. A. Forward and his co-workers were successful inapplying this process on a large industrial scale1, 2. This process is used in FortSaskatchewan to produce about 15,000 tons of Ni per year. In Berlin, investigationswere started on leaching with acid solutions3, 4. This process had also been used on alarge industrial scale in the D.S.A., but the choice of unfavourable working conditionsled to great difficulties, and to giving up this process for industrial use.

Later on in Berlin work was carried out especially on the kinetics of pressureleaching5, 6, 7, 8, 9 and its applications to the processing of smelter by-products, inparticular of mattes and speisses1O, 11, 12, 13, 14.

The dissolution of ores and by-products can be subdivided into four steps:I. the efficient dispersion of the gas, so that its dissolution occurs over as great

a surface area as possible, since only the dissolved oxygen reacts with thesolid,

2. the suspension of the solid, so that the entire surface can take part in thereaction,

3. the phase boundary reaction,4. the removal of the reaction products.The first two steps belong to the field of process engineering and will be discussed

from this point of view. The aim of these experiments15 was to find out first of allthe limits of efficiency of self-sucking stirrers in solutions of low viscosity with regardto the mass transfer. In addition, the effect of ultrasonics in the same reaction systemwas studied.

The experiments were carried out in a lucite container as shown in Fig. 1. Fourbaffles of O. 1 d width were in the stirring vessel. The height of these baffles wasadjustable. For every experiment one litre of liquid was used. An infinitely variabledirect current motor, which was fixed with a hollow shaft, served as the drivingpower for the stirrer.

*Head Professor of Extractive Metallurgy, Technical University of Berlin-West.

tThis paper was delivered at a meeting of the Institute on 22nd October, 1968.

July, 1969 Journal of the South African Institute of Mining and MetallurgyResearch in pressure /eaching-Franz E. Paw/ek

633

Sluffing/HI.

hollow sho't

".",.s

1-...... mi.ing r.ssel

osbestospocltoge

~fte'OS";e';r.',oftsduee,

Fig. 1-Fxperimental:equipmeot

In order to be able to determine the amount of gas taken in by the hollowstirrer, the suction hole of the hollow shaft was connected to a stuffing box with agas-flow meter attached. In addition, it was possible to feed the hollow stirrer duringthe experiments with oxygen out of a pressure tank, so that the amount of gas couldbe regulated independently of the natural suction of the stirrer.

For experiments on the influence of ultrasonics, the stamp-like, sound-radiatingpart of the oscillator was built in to the bottom of the stirring vessel, so that theflow conditions were not altered and exact comparisons could be made.

As a model for the mass transfer from gas to liquid the reactionS032- + 1/2 O2 --->-SOl- was used, which proceeds so rapidly, that the rate limiting

634 Journal of the South African Institute of Mining and Metallurgy

Research in pressure leaching-Franz E. PawlekJuly, 1969

step is the dissolution of oxygen. The dissolution of solid iodine in very diluteaqueous Na2S2O3-solution served as a model for the mass transfer from solid to liquid.

The leaching of Cu3As in ammoniacal solution with oxygen was chosen as themodel for dissolution processes in which all three phases are involved. The lowactivation energy of about 4.4 kcaljMol indicates that diffusion exerts the maininfluence12.

First of all the dissolution of molecular oxygen in the solution will be considered.The first requirement is a sufficient solubility of the gas in the liquid. The solubilityis determined by the temperature, independently of the partial pressure, and showsa minimum (Fig. 2). Other compounds dissolved in water, such as acids, bases orsalts, likewise decrease the solubility of the oxygen, as shown in Fig. 3.

E-0,~0

i.~-~Qacs-

~E~.So,O

~'--'-.Q~ 0,010

V)

c

0

Wink/er (45)

Himme/b/au(J1)

00 100T~mp~rotur~

200°c

Fig. 2-So1ubility of 0, in water as a function of temperature

, July, 1969 Journal of the South African Institute of Mining and MetallurgyResearch in pre>slIre leaching-Franz E. Pawlek

635

If~~-~:Q::t-a

".-... ...-...-...

J~ Q8

~~""""'"

~eo 0.6

oqu~ous solutions of

NHJH2S/J,CuS/J,

No OH(NH,J2S0,

Q' -'-. '-.0,2

0 , 2conu'nlral;on in moll'

J ,

Fig. 3-Solubility of 0, in different aqueous solutions

Furthermore, the rate of this step can be limited by a deficiency of suppliedoxygen. Altogether six different types of stirrers were tested, which are presentedschematically in Fig. 4. They suck different amounts of gas as a function of the rotationspeed as Fig. 5 shows. The letters in Fig. 5 correspond to the different stirrer typesas drawn in Fig. 4.

Not only the amount of gas, but also the diameter of the bubbles is dependenton the rotation speed. Fig. 6 shows a gas-liquid mixture with a gas flow rate of90 Normal litres per hour. The enlargement of a detail in Fig. 7 shows clearly thesingle bubbles. The analysis of numerous experiments led to the curve in Fig. 8,which indicates, that the bubbles reach a minimum size of about 0.05 mm in diameter.A further increase of rotation speed has no more effect.

tit U iflurbin~ imp~lI~r Iyp~ A lurb;n~ imp~lI~r typ~ B

* +J! E:=ia

modi fi~d tub. imp~lI~r Clurbin. imp~lI~r Bm

& y6

~triang/~ imp('lI~r 0 mann~ prop~lI~r p

636 Journal of the South African Institute of Mining and MetallurgyResearch in pressure /eaching-Franz E. Paw/ek

July, 1969

* di",lion o(*rotation

Fig. 4-Stirrer types

- 160I.c:.....

~c: 120'-c:0'- 80-u:..,.

~'-0


637

8-A-0 cmR-A = 2,.5 cm

400

A600 800 7000

sp~~d of rolol ion In1200

min-1

200

~

Fig, S-Air suction as a function of speed of rotation

-----

638 Journal of the South African Institute of Mining and MetallurgyResearch in pressure leaching-Franz E. Pawlek

July, .1969

Fig. 6-Gas-liquid mixture in equipment

-----

July, 1969 Journal of the South African Institute of Mining and MetallurgyResearch in pressure leaching-Franz E. Pawlek

639

Fig. 7-Gas-liquid mixture in equipment

Two factors have to be considered for the transport of dissolved oxygen to thesolid's surface: the degree of suspension of the solid and the blocking of the freereaction surface by gas bubbles. If the solid is completely suspended by the stirringeffect, further increase of rotation speed has almost no more influence on the dis-solution rate. The application of ultrasonics is only efficient, if the degree of suspensionis not maximum, because then an additional suspension effect occurs, as shown inFig. 9. The small effect of ca. 30 per cent increase of the dissolution rate can beexplained by an additional movement of the particles caused by the ultrasonic energy.

-- --------

8-A : 0 cmR-A . 1 cm

c : 31,5 9 ,/-1

1

aL : 90 NI'h-1

\" ~- -

640

E\I o,~c:,-'-.. Q6E0'-1)

" 0,'-~.a:)

..Q 0,2

~0-~ 2

.....

Journal of the South African Institute of Mining and MetallurgyResearch in pre;sure leaching-Franz E. Pawlek

July, 1969

200 «10 600 800 1000 1200speed of rotation in min-1

Fig. 8-Bubble size as a function of speed of rotation

,a-A:"cmR-A = 1 cm

3+

1400 800 1200 1600

speed of rotation in min-lFig. 9-Effect of ultrasonics as a function of speed of rotation

---


641

The effect of blocking of the surface by gas bubbles is shown in Fig. 10, whereleaching of CuaAs was carried out at a constant rotation speed, but with increasingamounts of O2' With increasing amounts of oxygen under the chosen conditions,there is an increase in the rate of dissolution up to a value of 70 normal litres per hour,after which there is a decrease caused by surface blocking by gas bubbles. The efficiencyof utilization of the oxygen is also strongly decreased, because intsead of many smallbubbles just a few big ones with a smaller surface area are formed.

~

-"

le: fJ,18- '-e e0) - 0.c: ,"- :)~ u2 Ot- e: 0,10

'-

e:'-

!I~

0,060

a-AR-A

n =

"--.(j)

'l°2

= 'cm=. 1 cm

800 rpm-I(2) m

~e:"'-~

80 '-0 ~

'-.

e:'0 "0)

~lie

0

50 100 150 200 250 JOOair f/owrot, inNL.h-l

0

Fig. to-Leaching rate and oxygen efficiency as a function of tbe air flowrate

Under ideal conditions and with certain assumptions, such as the perfectspherical shape of the gas bubbles and the closest packing of spheres, one cancalculate, that the time spent in the liquid is approximately 13 sec and that theiraverage ascension speed is about 1. 1 cm/sec.

For the investigation of events at the phase boundary, a mineral was chosen,which had the simplest possible composition. This was a very pure blende from Spainwith 67, 0 per cent Zn, 31. 6 per cent S, O.6 per cent Cu, and no iron or other heavymetals. The experiments16 were first carried out under the technical conditionsd 110°C, 10 atm 02-pressure for a two hour period. It was a disappointment to findout, that only 12 per cent of the theoretically possible amount had dissolved underthese conditions.

It was shown in all experiments, that H2S was formed from the beginning, sothat one may with certainty assume, that the first reaction is

ZnS + H2SO4~ ZnS04 + H2S

One can also imagine this as an electrochemical reaction and thereby assume thefollowing scheme (Fig. 11).


July, 1969

Anod. 50="

Zn SO.," 5ZnS 2.-

+2.- 2 H~ ., 1/2 °l

Kolhode - Hl0

Fig. ll-F.!ectrochemical model of the dissolution of ZnS

In this scheme it is mandatory, that electron transport can take place in thesolid. Zincblende is a semi-conductor and so at room temperature it is almost aninsulator. Its specific resistance was found to be 6 X 109 Qcm at 90°C. Before areaction on the surface of the solid can take place, oxygen molecules from the solutionmust be adsorbed. The reacting gas is bound to the surface by mutual exchange orby electron exchange. A theory of boundary chemisorption has been developed toexplain these events. According to this theory, the number of charge carriers in thesemiconductor can be enlarged by the presence of foreign atoms (electron donors),by the addition of extra chemical substances to the solution (Redox-systems), or bythe raising of electrons from the valence band to the conductivity band by means ofirradiation.

The influence of DV was first studied. It was necessary to work at a pressureof 1 atm and at 70°C because of technical limitations. The results are shown in Fig. 12.With pure ZnS, the energy difference between the valence band and the conductivityband is so large, that the DV irradiation cannot span the difference, only after dopingcan this be achieved. The reaction results are in agreement with this: pure ZnS doesnot react to DV irradiation, while doped ZnS shows a considerable increase insolubility.

aPc:.- 15

'b

"~-0'"'""-'b

V)


643

25

5

ZnS dop~d withoutUV

20

1O

- with UVwithou t

Zn 5 UVpr~cipitotPd

180

-0 3D 60 !JO 120 150

limp in minutP5Fig. 12-lnlluence of DV on tbe dissolution of ZnS

Electrons can also be supplied by a Redox system. In this experiment the Redoxsystem was formed by the addition of Fe3+, Cu2+,I2, TP+ and Ce4+. The expectedresult for iron is demonstrated in Fig. 13. The addition of an amount of Fe+3 corres-ponding to 10 per cent of the total weight of the used zincblende results in a five-foldincrease in the dissolution rate. The addition of copper shows a weak influence,while all other additions were either destroyed or precipitated by H2S.

Fig. 14 shows, that concentrates of zincblende contain varying amounts of iron.The extraction values correspond with one exception to the iron content of theconcentrates. Both of the concentrates with more than 10 per cent iron were inves-tigated by means of X-ray analysis, which showed, that the poorly soluble concentratescontained the iron as a solid solution, while the highly soluble concentrates containedthe iron in the form of pyrites or pyrrhotites. This .indicates, that Fe is not effectiveas a donor in the zincblende lattice.

.

--.-.---.--

0.50 '00.'O%Fe8 S %Fe

0.40 BO- 2 .s%F e:::: 60

0 %FeE )(~c

O.JO 60 c.- -C C0 0.- .-- .." "et 0.20 '0 e'" '".. -ac ..q, Q,I ,

C C~0.10 20


July, 1969

0.000 60

time"D 180

in minuttls2'0

0

Fig. 13-Influence of Fe on the dissolution of ZnS

~ ~~-

July, 1969 Journal of the South African Institute of Mining and Metallurgy 645Research in pressure leuching-Franz E. Pawlek

Analysis Fe ZnConce ntra te CaO diss. diss.

Zn'o Fe'o % % % Cu%

Prealpina 58,8 0,7 3,0 14,5 0,17

Minerva 60,5 2,25 1,6 33, 1 17,5 0,08

Gailitz 58,3 2,42 2,68 38,9 16,8 0,12

Pyhisalmi 54,9 8,3 41,7 36,0 0,33

Kassandra 52,7 8,5 24,2 38,0 0,84

Meggen 47,0 10,0 52,0 65,2 0,10

Cartagena 54, 75 10,25 43,4 23,0 0,51

Brunswick 49,5 11,8 28,8 72,3 0,10Fig. 14-Analysis of zincblende concentrates

However, it was found that sulfides with a considerably higher electric conduc-tivity by no means dissolved faster than the poor semi-conductor ZnS. There musttherefore be still another factor hindering dissolution. This was found to be theH2S which is formed during the leaching. Fig. 15 shows, that the continual removalof H2S can increase the leaching rate approximately 4-fold, while adding H2S at apressure of 2 atm can completely suppress the reaction. This is due to the fact, thatan equilibrium occurs in the reaction

ZnS + H2SO4::;::ZnSO4 + H2S

This equilibrium brings the reaction to a stop. From the approximate data in theabove mentioned case, an equilibrium pressure of ca O.5 atm H2S can be calculated,which agrees well with the experimental results. The removal of H2S can in principlebe accomplished according to the equations in Fig. 16. The first reaction takes placeonly at very high concentrations of H2SO4, the third reaction apparently takes placeonly at very high temperatures. The middle reaction takes place only very slowly,and the problem is to accelerate it. It has been known for a long time, that oxidationreactions can be accelerated by activated carbon. This has been used successfully forthe oxidation of H2S to So. Fig. 17 shows that ;1~tivated carbon can increase theoxidation of H2S and thereby the leaching rate of zincblende by a factor of approx. 5.

-----

0.20 '0. H2S -removal. p~= 10 at~-

~P02= ID at0 0.75 . 30 c:e "-.,. PH2S = 2atc: c:

0"- "-c: ....0 e"- 0...

0.70 20 "'-" ...Cl lie

... q,...lie I. c:I

~~0.05 la

H25 + H250, . H2S03+ H2O + 5.

2 H25 + °2 . 2 5 0 + 2 H2O

H25 + 2 °2 . 50,--+21:1+

646 Journal of the South African Institute of Mining and MetallurgyResearch in pressure /eaching-Franz E. Paw/ek

July, 1969

2 tlI HAS

30 60 90 120time in minutes

0.00' 00 15([

Fig. IS-Influence of H,S on tbe dissolution of ZnS

Fig. 16-PossibJe oxidation reactions for H,S


647

IOD

90

80+509 acli~ol

carbon

'b~ 60-0.,..,. 50"-'b

"'40~

atc 70"-

0 60 120 180 2'0 300

lim. in minul.sFig. 17-Inftuence of activated carbon on the dissolution of ZnS


July, 1969

As shown in Fig. 18, the leaching rate of most of the other sulfides is also stronglyinfluenced by the oxidation rate of H2S, but at the same time one has to conclude,that there must be a third factor of importance besides the electric conductivity andthe acceleration of the oxidation of H2S, namely the atomic structure of the com-ponents. Fig. 19 shows an attempt to co-ordinate the atomic structure, the co-ordination number and the electrical resistance. However, it is not convincing,because we still know too little about the atomic bonding conditions, especiallyabout the relative proportions of covalent and ionic bonds. It is striking, that theleaching of chalcopyrite (CuFeS2) is exceptionally difficu1t17.Economical leaching isonly possible by either destroying the structure by means of heating and distillingpart of the sulphur away or by the reaction with cement copper. At temperatures ofmore than 160°C the dissolution apparently occurs by quite a different mechanism.Fig. 20 shows that a great increase of the dissolution rate occurs above this temperatureand that, instead of the primarily formed H2S, now SO42-arises. A stepwise oxidationof the H2S through So to SO42- can be excluded because of the very slow second step.There are no explanations yet for this phenomenon.

'DD

so

~c: 60'-c:Q

'--"~ '0..Cl.

-III-Cl.10E

Ff>S20

0 JO 60 90 '20timf' in minutf>S

'00 -«J

60

'0

'500

0 JO 60 90 t20timf' in minutes

,so

Fig. IS-Leaching rate of different metal-sulphides

-------

coordinati.n 4 4/1 6"ItUmOffr

resisti. .'SSII-rit, lut;.n 9 % !/ % , %r (Qcm) %

lnS 1"0" NiJS, '.10-1 30 fIbS 5.10' 15 CuJAs 1.",-1 100

z"Se r.s.'0' 15 CuS , . 10-1 1( FeS 2.'0' ,DO

Zn re 2.' 104 'DO NiS 2.10'" 18

ZnS 1.10' , As-As Ca4sS I.roo 26S-S

Cu,FeSnS4 1.102 14 SoSFeS2 roo J6SoS

CuFeS, J. '0' 5 iAs-s FeAsS roo JI~s-S

Cu3SU4 7.10° ID stat. NiAsS HO.2 JJ5b-S NISOS 2102 65SII-S

. Zn5 diss.

SO, --. formed

. H25 formed


649

Data of Diuo/ution arHI Rv.isti.,i,i.s

"'"",er.ture : '0° C time; I lIour

Fig. 19-Data of dissolution and resistivities

0.20

-......-0Ec:"-

0.15

c:0'--Q'"-c:--"c:0

"

010

0.05

0.0070 90 110 130 150

t.mp.rotur. in . C

170 190

Fig. 20-Influence of temperature on the reaction occurring at the leaching of ZnS

~~

100

0£ 8001<:)<:)-........

60III-0.c:Q.-;)\11

200

"0100

Ci,

E

01


July, 1969

The last step in the leaching process is the removal of reaction products fromthe surface of the solid. In this regard it is important to consider, that the solubilityof the sulfate formed decreases greatly at high temperatures18 (Fig. 21). In particular,FeS04 is already completely insoluble at 160°C.

Finally, two examples of the use of pressure leaching for the processing ofsmelter by-products will be described19.

During the processing of copper dross in lead refining, a lead-copper-matte isformed. Its composition and leachability at 100°C and 10 atm O2 is shown in Fig. 22.The X-ray analysis of the matte indicates ZnS, PbS and CuFeS2-x. The residue ofthe leaching process consists of PbS04 and So in addition to small particles of undis-solved matte. In Fig. 23 a possible flow sheet is presented.

~ 00

Tt.>mpt.>rofurt.> in 0 CFig. 21-Solubility of some metal-sulphates as a function of temperature


651

Prusur~ fc>aching of Cu.Pb-Ma"~ 0 9

Anolysis Cu:J2.2%. Pb: 26.S %. F.:".2 %.5:'8.8%

Conditions; H250,=60gl'. POJ'Oot;_T~'OO°Csoli d: liquid = 1: 20mot.riol <: 60.}Jm

16100 % Cu - -

..--

" ~

6

x-x Cu-Extraction0-0 F~ Ex traction

Q,

~ 12-"a.

t':

"2

30 60 90 120- , Cm;n}Fig. 22-Pressure leacbiug of Cu-Pb-matte


July, 1969

Hldrom~to"urg;col Tr~otm~nt of Cu-Pb-Molt~

/PrE'Ssurf' Lf'OChin~

~ IFiltE'r;ng I

+-..I RE'siduf'I ~

I Su/fur Ex tractionI with CS2IIIIIIIII,

r..cyc IE'J

1.

2.

Solution

J. F~- and As-Prf'cipi-totion with Co(OH)

~

I Filt~

ITo;Iings

501 u tion

1

[ Elf'ctrolysis )IIIL - H}501,

(60 g/I H2S01, . P02-10ot,T = 800 C )

solid: liquid = I : ID

~

IFill~

IElf'mftntorlSulfur

Rftsiduft to Pb -Blost-FurnocE' or Sintftring

Fig. 23-HydrometaUnrgical treatment of Cu-Pb-matte

Finally, speisses, as they occur in lead smelting, have been subjected to pressureleaching. The compounds shown in Fig. 24 were found to be components of thespeisses by means of X-rays 20, 21, 22. In model experiments it was shown, thatarsenides go into solution much easier than sulfides. NiAs, for instance, is completelydissolved under much milder conditions, such as two hours at 60°C and I atm O2'The problem in processing speiss is the removal of arsenic. Since arsenic is oxidizedto HAs042- by pressure leaching in alkaline solutions and since this compound canbe easily converted into an insoluble substance, alkaline leaching was also inves-tigated. A summary of the components of speiss and the yield of the most importantsubstances after the different leaching processes is given in Fig. 25. The acid leachinghas an advantage, because on account of the mild leaching conditions all the noble

1,.

5.

N~/o/s Cu, Pb

Sulf; dflsAg, Au

CU]S, F~S, PbS

Ars#nidflS Ni As, NisAS], Ni"As8,Sb, Sn,

F~As, F~ ]As,Co

Cu]As

EI(>m(>nl H2501, NHJ +(NHI,J2501, No OH Conlt>nls of5Dt>;SS127

Cu 100,0 % 92,S % 1,8 % 25,9 %

Ni 100,0 % ~"9 % - 10,9 %Co 100,0 % n.d. - 2,7 %As 65,0 % 5J,8 % 2J,8 % 27,7 %

Pb - n. d. 81,0 % 15,7 %


653

metals in heavy decomposable sulfides remain as such in the residue and can beseparated from the lighter sulfates and basic salts of Pb, Sb and Sn in a hydrocyc1one.The sulfides go to a copper smelter, the sulfates of the residue to a lead smelter andthe leaching solution can be separated from arsenic by means of concentration byevaporation (Fig. 26).

With ammoniacal leaching there is the disadvantage, that a distribution of silverbetween the solution and the residue occurs. Therefore it is not recommended,pending further study.

At the end I would like to thank the "Deutsche Forschungsgemeinschaft", theSenator of Economics in Berlin and the Federal Ministry of Economics for sponsoringthese investigations.

Consliluf'nls of Spf'issf's

Fig. 24-Constituents of speisses

Prt>ssurt> LNlching of 5p(>iss 127 in H2501" NHJ +(NHI,)2S01,

P02: 10 01, T=80°C, 1:120m;n, 100gl1 5pt>;ss

H2501, : co. 2,1,5 moll INHJ = co. 5,8 molll +(NHI,J2501, : 1,5 molllNo OH = co. 2,5 molll

and NoOH

Fig. 2S-Pressure leaching of speiss

--------


July, 1969

Hldrom~lolI ur,icol TrHlm~nl of Sp~;sus

ol wilh H2S0,

, IPtI'ssure leoching I

1

(',"molll H:JS°"Po" '001, T=BO'Ct. 120min,solid:liquid:t:10

b) INi th HHJ olld (Nlicl,SO,

"P,.ssu,e leoehing (5.8mo/l1 HHJ

-'.5 mol//fNIic},SO,Po, =lOot. T. eo'C.t ,

'20 min,solId, lIquId. I 10

, IFiIte'i~,I'

Solution Residue(Cu,Co,Hi,Asl 0 (Pb, Sn,Sb, Ag-Aul

!

2'IF~'erinz

Solution Residue(Cu,CQ,Ni,As (Pb.Sn.Sb.Assome Ag-Au} Res/oIAg.Au)

IConcent,otion bleropo,otion

As -Prec;pitotion os

CoJ(As~l, or os/rig NH, .150, . f H2O

'1J,IFitteringl

'/~As -lIeo,ingH,sO,

CII-, Co-, Hi -SlIlfotes

Conrelltionol hld,ometollll",coltreotmellt 01 t"e Cu, Co, GIld

Ni beorillg solllt'OIl

Fig. 26-HydrometalIurgical treatment of speisses

REFERENCES

1. FORWARD, F. A. and MACKIW, V. N. AIME Trans. 203 (1955), 457/63,2. FORWARD, F. A. and HALPERN, J. Tram. Inst. Min. Met. 66 (1956/57), 401/18.3. NEUHAUS, H. and PAWLEK, F. Metall u.Erz 6 (1953), 41/44.4. PAWLEK, F. and PIETSCH, H. Erzmetall, 10 (1957), 373/83.5. GERLACH, J. Z. Metall, 16 (1962),1171/79.6. GERLACH, J. Z. Metall, 17 (1963), 32/35.7. GERLACH, J., HAHNE, H. and PAWLEK, F. Erzmetall, 18 (1965), 73/79.8. GERLACH, J., HAHNE, H. and PAWLEK, F. Erzmetall, 19 (1966),66/74.9. GERLACH, J., HAHNE, H. and PAWLEK, F. Erzmetall, 19 (1966), 173/80.

10. LYDTIN, H. J. Diss. TU Berlin 1961.11. FRIES, H., GERLACH, J. and PAWLEK, F. Erzmetall, 18 (1965),509/14.12. GERLACH, J., PAWLEK, F. and TRAULSEN, H. Erzmetall, 18 (1965), 605/12.13. PAWLEK, F., GERLACH, J. and DAHMS, J. Erzmetall, 20 (1967), 203/08.14. GERLACH, J. and PAWLEK, F. 'Pressure leaching of speiss', Unit processes in hydrometallurgy,

Dallas, Texas, Febr. 25-28, 1963, 308/25, Gordon and Breach Science Publishers, New York,London.

15. PAWLEK, F. BIMLER, U. and WUTH, W. Verfahrenstechnik 2 (1968) 12, 513/19.16. EXNER, F. Diss. TU Berlin, to be published.17. RODEL, R. unpublished.18. BRUHN, G., GERLACH, J. and PAWLEK, F. Z.fanorg.u.allgem. Chem. 337 (1965),68/79.19. Unpublished.20. HENNIG, U. and PAWLEK, F. Mh.fChem. 95 (1964),322/27.21. HENNIG, U. and PAWLEK, F. Erzmetall18 (1965), 395/403.22. HENNIG, U. and PAWLEK, F. Erzmetall18 (1965), 293/297.

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