ORIGINAL ARTICLE

c

I.M. Ahmed, A.A. Nayl *,1,2, J.A. Daoud

Hot Laboratories Centre, Atomic E

Received 24 February 2012; accepte

H2SO4 leaching here the percent recovery amounts to 95% and 99% for zinc and copper, respectively. The exper-

and a ow sheet were developed and tested to separate zinc, copper, iron, aluminum and silica gel

2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction

has inevitably resulted in an increased ux of metallic

substances in the environment. Recovery and extraction of these

metals is necessary and important both from an economic

Dessouky et al., 2008). Ores, secondary materials, wastes,

ground samples of spent particles of boat paint was studiedby Jessop and Turner (2011). Huge quantities of slag, which

is a waste by-product of smelting and converting operationsin metallurgical plants, is posing a potential environmentalthreat due to entrained values of base metals and sulfur. High

temperature pressure oxidative acid leaching of nickel smelterslags was investigated as a process to facilitate slag cleaningand selective dissolution of base metals for economic recovery(Yunjiao et al., 2008). Hydrometallurgical process to recover

E-mail address: aanayl@yahoo.com (A.A. Nayl).1 Permanent address: Hot Laboratories Center, Atomic Energy

Authority. P.O. 13759, Cairo, Egypt.2 Chemistry Department, College of Science, Al-Jouf University,

2014 Sakakh, Kingdom of Saudi Arabia.

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

Journal of Saudi Chemical Society (2012) xxx, xxxxxx

King Saud

Journal of Saudi C

www.ksuwww.scienceetc. are the most important sources for some metals like cop-

per, nickel, cobalt and zinc. The leaching of Cu and Zn from* Corresponding author.The increasing demand of zinc and copper in the world has re-quired intensive studies for the recovery and extraction ofthese metals from different sources. Also, the tremendous in-

crease in the use of these metals over the past few decades

point of view and due to the increased requirement for envi-ronmental protection. Therefore, it is essential to remove theseelements from industrial efuents and radioactive wastes be-

fore discharging into natural water bodies or onto land (Elfrom the brass slag.imental data of this leaching process were well interpreted with the shrinking core model under

chemically controlled processes. The apparent activation energy for the leaching of zinc has been

evaluated using the Arrhenius expression. Based on the experimental results, a separation method13

ht

PJKEYWORDS

Recovery;

Brass slag;

Zinc;

Copper;19-6103 2012 King Saud Utp://dx.doi.org/10.1016/j.jscs.

lease cite this article in prournal of Saudi Chemicalo

wniversity

2012.11.0

ess as: ASocietynergy Authority, Post Code 13759 Cairo, Egypt

d 14 November 2012

Abstract Leaching and recovery processes for zinc and copper from brass slag by sulfuric acid

were carried out and iron and aluminum were also precipitated as hydroxides in addition to silica

gel. The factors affecting the performance and efciency of the leaching process; such as agitation

rate, leaching time, acid concentration and temperature were separately investigated. The results

btained revealed that zinc and copper are successfully recovered from these secondary resources,Leaching and recovery of zinby sulfuric acid. Production and hosting by Elsev

03

hmed, I.M. et al., Leaching an(2012), http://dx.doi.org/10.10and copper from brass slag

University

hemical Society

.edu.sadirect.comier B.V. All rights reserved.

d recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

different conditions, the average process efciency values were

Shimadzu UV/VIS, double beam recording spectrophotome-ter, Model 160-A, Japan.

Mineralogical analysis of the sample was determined by

XRD using a Shimadzu-6000) (Japan) diffractometer. Theconditions of these measurements were obtained using Cu-Ka radiation and Ni lter. Analysis of the diffraction patternswas made by the whole powder pattern-tting computer pro-

gram intra-connected to the system.The hydrogen ion concentration for the solutions was mea-

sured using a digital pH meter of the Hanna instruments type

at the ambient laboratory temperature of 25 1C.

2.2. Leaching of slag

In the leaching process, 5 g of ground slag that was below

Table 1 Chemical composition of the brass slag.

Element Zn* Cu* Fe* Al* Si* Cl Ca

Contents 69 13 1.3 4.4 6.0 4.6 1.7

* Present as oxides.

0 100 200 300 400 5005

Agitation rate, rpm

Figure 1 Effect of agitation rate on the recovery of zinc and

copper. Leaching time = 10 min, L/S = 5, [H2SO4] = 30%,

temp. = 35 C.

2 I.M. Ahmed et al.variable (Lopez et al., 1988) However, the hydrometallurgicalrecovery of zinc metal or its salts was also described in the lit-erature by Barrett et al. (Barrett and Nenniger, 1992; Barrett

et al., 1992). The leaching of zinc from a sphalerite concentrateusing hydrogen peroxide as an oxidant in sulfuric acid solu-tions was examined by Pecina et al. (2008). A study was per-

formed to assess the inuence of different factors such asacid and peroxide concentrations, particle size, reaction time,and temperature on zinc dissolution kinetics and the global

reaction rate is governed by the chemical reaction rate. Shiba-saki and Hasegawa (1992) carried out a combined hydrometal-lurgical treatment of copper smelter dust and lead smelter

copper dross. It was shown that about 80% of the copper inthe dross could be extracted at 80C with 200 kg/m3 sulfuricacid; 150 kg solid/m3 and 46 h of leaching under oxidizingconditions. In comparison, the leaching of the copper smelter

dust was relatively easy. Bzura (1979), studied the recoveryof all metal values from brass foundry skimmings containing>85% metals, primarily copper and zinc in alloyed form

and zinc oxide. The skimmings were crushed, ball milled andreacted with HCl and sulfuric acid at pH 0.11.5. The resultingsolution of zinc salts was continuously separated.

In Egypt, several types of zinc-containing waste materialsare available. These include zinc scrap, spent dry cell batteries;zinc dross, resulting from the zinc cathode industry, and zinc

ash, obtained from galvanizing processes. The latter two mate-rials contain chlorides, which render the recovery of zinc bysulfuric acid electrowinning unsuitable (Rabah and EI-Sayed,1995).

Different processes, such as cementation, can be used to re-move and separate Cu2+ from different solutions and fromleach solutions.

The aim of this work is to recover and separate metal valuessuch as zinc and copper from brass by applying a hydrometal-lurgical method using sulfuric acid as the leaching agent. Dif-

ferent parameters affecting the recovery processes such asagitation rate, leaching time, acid concentration, liquid/solidmass ratio, and temperature of the system were investigated.Kinetics of the system and preliminary economic study was

performed to evaluate the cost of the products compared tomarket prices. A ow sheet is developed and tested to producehigh purity metal oxides.

2. Experimental

2.1. Materials

The slag sample used in this investigation is given from a brass

manufacturing plant in Cairo, Egypt, whose chemical compo-sition is given in Table 1 determined by Energy DispersiveX-ray. The concentration of the metals were estimated usingand recycle metals from the wastes of brass which contain cop-per, zinc and lead using different leaching agents including sul-furic acid, ammonia, hydrochloric acid, cyanide and acetic

acid was developed by Nesbitt and Xue (1995). It is reportedthat sulfuric acid containing copper sulfate with dissolved oxy-gen is the most successful leaching agent (Sharma and Row,

1985).The pyrometallurgical recovery of zinc from secondary re-

sources using different waste materials has been studied underPlease cite this article in press as: Ahmed, I.M. et al., Leaching anJournal of Saudi Chemical Society (2012), http://dx.doi.org/10.10100 lm and was not exposed to any metallurgical pre-treat-ment operation was added to 25 g of 30% H2SO4 for 10 min

in 250 ml conical ask with an agitation rate of 150 rpm at35C unless otherwise said. One milliliter solution samplewas taken using a syringe lter of 1 mm pore size. The sampleswere chemically analyzed for the determination of zinc and

copper content. After that, the percentage recovery of zincand copper was calculated.

3. Results and discussion

3.1. Leaching

3.1.1. Effect of agitation rate

The results of the effect of agitation rate on zinc and copperdissolution by 30% H2SO4 with leaching time 10 min and at

10

40

60

80

100

Zn Cu

Rec

over

y (%

)d recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

35C investigated in the range of 60400 rpm with liquid/solidmass ratio of 5/1 are shown in Fig. 1. The presented data showthat the recovery of zinc was increased from 60% at 50 rpm to

around 93% at 150 rpm and the recovery of copper was keptaround 9% with various stirring speeds. Therefore, the disso-lution process does not seem to be controlled by mass transfer

through the liquid boundary layer, despite the change in solu-tion viscosity caused by the formation of silica gel. As a result,the agitation rate was kept at 150 rpm, unless otherwise stated.

3.1.2. Effect of leaching time

The effect of leaching time on the leaching of 5 g of slag using25 g of 30% H2SO4, keeping the agitation rate at 150 rpm and

temperature at 35C, was studied in the range of 580 min,Fig. 2. It is clear that the recovery of zinc increases withincreasing time up to 10 min then decreases with a further in-

crease in time. The recovery of copper increased with time upto 30 min where it reached 95% then decreased with a furtherincrease in time. This behavior may be due to the competitionbetween zinc and copper ions in solution. Besides, with

increasing time up to 10 min, both iron and aluminum werecompletely leached whereas less than 10% of copper was lea-ched and silica made the leached solution more viscous.

0 10 20 30 40 500

20

40

60

80

100

[H2SO4], %

Zn Cu

Rec

over

y (%

)

Figure 3 Effect of acid concentration on the recovery of zinc and

copper leaching time = 10 min, L/S = 5, temp. = 35 C, agita-tion rate = 150 rpm.

2 3 4 5 6 7 80

5

10

40

60

80

100

Zn Cu

Rec

over

y (%

)

Liquid : solid ratio, mL : gm dust

Figure 4 Effect of liquid: solid ratio on the recovery of zinc and

copper from brass slag. [H2SO4] = 30%, leaching time = 10 min,

temp. = 35 C, agitation rate = 150 rpm.

Leaching and recovery of zinc and copper from brass slag by sulfuric acid 33.1.3. Effect of H2SO4 concentration

The effect of acid concentration was investigated in the rangeof 1050% (V/V) H2SO4 at a leaching time of 10 min, liquid

(L):solid (S) ratio = 5/1 at 35C and the results are presentedin Fig. 3. The extraction of zinc was found to increase with anincrease in acid concentration between 5% and 30% (V/V)

then decreased with a further increase in sulfuric acid concen-tration due to the competition caused by the leaching of cop-per at high acidity leading to an increase in the viscosity of

the solution that consequently inhibits the leaching process.This behavior was previously observed in H2SO4 medium(Bodas, 1996; Abdel-Aal, 2000; Espiari et al., 2006).

The effect of H2SO4, HNO3, H3PO4 and HCl concentra-

tions upon zinc dissolution from natural samples was studied

0 20 40 60 80 1000

20

40

60

80

100

ZnCu

Rec

over

y (%

)

Leaching Time, min.

Figure 2 Effect of leaching time on the recovery of zinc and

copper from the brass slag. L/S = 5, [H2SO4] = 30%,

temp. = 35 C, agitation rate = 150 rpm.Please cite this article in press as: Ahmed, I.M. et al., Leaching anJournal of Saudi Chemical Society (2012), http://dx.doi.org/10.10by Terry and Monhemius (1983). The authors observed thatthe rate of zinc dissolution is strongly dependent on both theacid (proton) concentration and the acidic anion(SO24 ;PO

34 , Cl

and NO3 ). The following reactivity orderwas observed by the study with respect to the acid anion:HCl HNO3 < HClO4 < H2SO4 H3PO4 and they sug-gested that the difference in the reactivity order is in a function

of the complex afnity for the zinc ion.

3.1.4. Effect of liquid/solid ratio

The effect of liquid/solid ratio (L/S) on the recovery of Zn(II)

and Cu(II) was investigated in the range 3/18/1 with leachingby 30% H2SO4 for 10 min at 35C with an agitation rate of150 rpm. The recovery percent was found to increase andd recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

70C seriously decreases zinc recovery due to possible poly-merization and hydrolysis.

3.1.6. Identication of the reaction mechanism

To identify the reaction mechanism of the leaching process ofzinc, the so-called reduced time plots were used. The leachingrates of zinc were analyzed with the shrinking core model for

reaction control under the assumption that the slag is a homo-geneous spherical solid phase (Levenspiel, 1972).

For the zinc leaching kinetic, two established kinetic models

were used, and expressed by the following equations:

1 1 a1=3 MkcCAt=dr k1t 11 21 a 31 a2=3 6uMDCAt=dr2 k2t 2

Eq. (1) is applicable to chemically controlled processes and

4 I.M. Ahmed et al.0

20

40

60

80

100

Zn Cu

Rec

over

y (%

)reached a maximum of 93% and 9%, at liquid/solid mass ratio5/1 for Zn and Cu, respectively, Fig. 4.

3.1.5. Effect of temperature

The effect of leaching temperature upon zinc and copper disso-lution was studied in the range 1070C while the other leach-ing parameters were xed at 30% H2SO4 and L/S mass ratio of5, Fig. 5.

It can be observed from the results obtained that the values

of the dissolution rate for zinc and copper increase withincreasing temperature till 35C for Zn and 70C for Cu.The low recovery amounts at low temperature is due to thelow reactivity of slag, while as the temperature increases, the

non-matching of zinc and copper recovery is due to partialhydrolysis of slag till 35C but increasing the temperature to

Eq. (2) to diffusion controlled processes through the porousproduct layer. where kc is the rst-order rate constant(m min1), M is the molecular weight of the solid reactant(kg mol1), CA is the acid concentration (mol m

3), D is thediffusion coefcient (m3 min1), d is the density of the particle(kg m3), r is the initial radius of the particle in (m), a is thefraction reacted at time t (min), k1 (m min

1) and k22 1

400 20 60 80

Temperature, oC

Figure 5 Effect of temperature on the recovery of zinc and

copper from brass slag [H2SO4] = 30%, leaching time = 10 min,

L/S = 5.

0 2 4 6 8 10 120.0

0.2

0.4

0.6

Temperature R2

10 oC 0.988 15 oC 0.933 20 oC 0.994 25 oC 0.995 35 oC 0.993

1-(1-

)1/3

Time (hr)

Figure 6 Plots of 1(1a)1/3 vs. time for zinc dissolution atvarious temperature in 30% H2SO4.

Please cite this article in press as: Ahmed, I.M. et al., Leaching anJournal of Saudi Chemical Society (2012), http://dx.doi.org/10.10(m min ) are the overall rate constants, and u is the stoichi-ometric coefcient

To determine which of the kinetic equations mentioned

above are applicable, the data presented in Fig. 5 are plottedaccording to Eqs. (1) and (2), respectively. The plots of theabove kinetic equations as a function of time showed that only

Eq. (1) gives perfectly straight lines from 0 to 10 min for zinc,but Eq. (2) does not, indicating that the dissolution reaction ofZn is controlled by the chemical reaction taking place on the

surface of the slag and H2SO4. Plots of the function1(1 a)1/3 vs. time at the leaching temperatures as shownin Fig. 6 indicate that the dissolution rates of zinc in the range035C is chemically controlled according to Eq. (1) This im-plies that, during the initial periods, the reaction uid can pen-etrate freely within the cracked and porous particles and theleaching reaction is not restricted to the core/product interface.

3.1 3.2 3.3 3.4 3.5 3.6-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

ln K

( 1/T ) x 103, ok

Figure 7 Arrhenius plot for Zn dissolution in 30% sulfuric acid

solution.d recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

was adjusted at 3.5 using NH4OH, whereas iron and aluminum

were precipitated as hydroxides in addition to silica gel. Zincsolution can be subjected to crystallization to obtain zinc sul-fate heptahydrate. Zinc can be precipitated as zinc carbonateat pH = 6.5 by adding Na2CO3. The copper residue is leached

with hydrochloric acid to obtain cupric acid solution that can

0.0 g

L

Zn,

)tatio

of z

Figure 9 XRD pattern of the slag before and after the leaching

process.

Leaching and recovery of zinc and copper from brass slag by sulfuric acid 5After that, the leaching of non-porous core of particles pro-gressed slowly and the kinetics appear to be limited by diffu-sion through the product layer.

3.1.7. Estimation of activation energy

The relation between the overall rate constant from Eq. (1) andtemperature may be expressed by the Arrhenius equation:

k A expEa=RT 3where k is the overall rate constant (m min1), A is the fre-quency factor (min1), Ea is the activation energy (J mol

1),R is the universal gas constant (8.314 J K1 mol1) and T isthe reaction temperature (K).

Rate constants for different temperatures were then plottedagainst the corresponding temperatures according to the

Arrhenius equations (Fig. 7). The apparent value of activationenergy (E) for the leaching of slag by H2SO4 was calculatedfrom the slope of the obtained straight line and found to beabout 59.0 2.7 kJ mol1 for zinc. The value of the activationenergy supports the proposed chemically controlled mecha-nism. This value is similar to those obtained by Terry andMonhemius (1983), that found 49.2 kJ/mol1 and 39.0 kJ/mol1

for the dissolution of natural and synthetic willemite samplesin sulfuric acid solution (pH = 1.9), respectively. Similarly,Teresa Pecina et al. (2008) found an activation energy of

50.0 kJ/mol. for the dissolution of zinc in sulfuric acid.

3.2. Cementation step

Brass smelter slag (10

Copper residue (

Leaching with HCl

CuCl2.2 H2O ( 25.3 g ) Zn, Cu (soln

Cemen

ZnSO4.7H2O

(Crystals), (250.0 g)

Figure 8 Proposed ow sheet for the sequential separationZinc dust and slag were used in stoichiometric ratio as cement-ing agents to remove copper from the leaching solution, within10 min at 25C where >99% of copper was removed. Coppercementation occurs according to the following reaction:

Cu2 Zn! Zn2 CuThe progress of the reaction was followed by the measure-

ment of free Cu2+ ions in the solution. It is reported thatcementation reactions mostly follow rst order kinetics (R).

3.3. Process ow sheet

The sequence of operations for the separation of zinc, copperfrom the studied slag is shown in Fig. 8. Using 30% (V/V)H2SO4 for selective leaching of zinc, the pH of the solution

Please cite this article in press as: Ahmed, I.M. et al., Leaching anJournal of Saudi Chemical Society (2012), http://dx.doi.org/10.10) (Zn, Cu, Fe, Al, )eaching with 30% H2SO4, 10 min.

Cu, Al, Fe), solution

Adjust the pH to 3.5 by NH4OH

Fe(OH)3 and Al(OH)3n by zinc dust (1.2 g)

Spongy Copper

(Powder), (1.1 g)

inc, copper, iron and aluminum from the brass smelter slag.be crystallized to get cupric chloride dihydrate.Mineralogical analysis of the slag before and after the

leaching process was determined by XRD as in Fig. 9. XRDanalysis for the slag before the leaching process indicated thatit contained two main constituents; namely zinc minerals

(Zn2SiO4 and ZnO), and copper oxide (CuO) with smallamounts of quartz (SiO2) and aluminum (Al2O3SiO2). How-ever, iron and other elements were present in trace amounts.

The analysis of the residue (slag sample after leaching process)indicated that it contained only quartz (SiO2) as the mainconstituent.

4. Conclusions

Leaching of brass slag to recover zinc and copper in sulfuricacid solutions was studied. It was found that the zinc

d recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

extraction was fast and increased with sulfuric acid concentra-tion. The shrinking core model with chemical control tted theexperimental results. The use of the grain model, which suc-

cessfully described the dissolution of zinc analysis of the zincsilicate particles, is suggested because there was no reactionproduct on the particle surfaces. The activation energy was

found to be 59.0 2.7 kJ/mol.

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zinc silicate ore. Hydrometallurgy 55 (3), 247254.

Barrett, E.C., Nenniger, E.H., 1992. Hydrometallurgical treatment of

electric arc furnace dusts. US Pat., 5,082,493.

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gical process to treat carbon steel electric arc furnace dust.

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Bzura, H., Can. Pat. 1,048,279, 13 February 1979, Appl. 235,437, 15

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El Dessouky, S.I., El-Nadi, Y.A., Ahmed, I.M., Saad, E.A., Daoud,

J.A., 2008. Solvent extraction separation of Zn(II), Fe(II), Fe(III)

and Cd(II) using tributylphosphate and CYANEX 921 in

kerosene from chloride medium. Chem. Eng. Process. 47, 177

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Espiari, S., Rashchi, Sadrnezhad, S.K., 2006. Hydrometallurgical

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Levenspiel, O., 1972. Chemical Reaction Engineering, second ed.

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zinc concentrate in H2SO4 solutions containing H2O2 and com-

plexing agents. Miner. Eng. 21, 2330.

Rabah, M.A., EI-Sayed, A.S., 1995. Recovery of zinc and some of its

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lurgy 37, 2332.

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Terry, B., Monhemius, a.J., 1983. Acid dissolution of willemite ((Zn,

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6 I.M. Ahmed et al.Please cite this article in press as: Ahmed, I.M. et al., Leaching anJournal of Saudi Chemical Society (2012), http://dx.doi.org/10.10d recovery of zinc and copper from brass slag by sulfuric acid.16/j.jscs.2012.11.003

Leaching and recovery of zinc and copper from brass slag by sulfuric acid1 Introduction2 Experimental2.1 Materials2.2 Leaching of slag

3 Results and discussion3.1 Leaching3.1.1 Effect of agitation rate3.1.2 Effect of leaching time3.1.3 Effect of H2SO4 concentration3.1.4 Effect of liquid/solid ratio3.1.5 Effect of temperature3.1.6 Identification of the reaction mechanism3.1.7 Estimation of activation energy

3.2 Cementation step3.3 Process flow sheet

4 ConclusionsReferences