142 Processing of Solution After Leaching Of

Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 142

PROCESSING OF SOLUTION AFTER LEACHING OF STEELMAKING DUST BY CEMENTATION

Marek Palenčár 1), František Kukurugya 1), Andrea Miškufová 1) 1)Technical University of Kosice, Faculty of Metallurgy, Department of Non-ferrous Metals and Waste Treatment, Slovakia

Received: 09.01.2015 Accepted: 04.05.2015

*Corresponding author: e-mail: [email protected], Tel.: +421 55 602 2426, Department of Non-ferrous Metals and Waste Treatment, Faculty of Metallurgy, Technical University of Košice, Letná 9, 04200 Košice, Slovakia

Abstract The work includes a description of a hydrometallurgical processing of steelmaking dust a waste product of steel production from electric arc furnace (EAF). Most attention is paid to cementation. The aim is to study purification of solution by cementation of impurities that could cause problems in zinc electrowinning process. Most attention is focused on removal of cadmium and lead from the sulphate and chloride solutions. The highest efficiency of cadmium removal was achieved in the sulphate solution, at 25, 50, 80 °C and at pH = 4, 5, 6. The highest efficiency of lead removal from sulphate solution (87.61 %) was achieved at pH = 6 and temperature of 80 °C. In chloride solution, the highest efficiency of lead removal (99.94 %), at the same pH but at a lower temperature of 50 °C was achieved.

Keywords: Steelmaking dust, hydrometallurgy, cementation, lead, cadmium, zinc powder, purification

1 Introduction Steelmaking production is accompanied by generation of different kinds of waste. Except a slag and emission, sludge and steelmaking dust, which consist of mainly iron oxides, are generated. When a scrap is melted, volatile elements like zinc, cadmium and lead, get into a steelmaking dust [1]. Input material in EAF varies by its composition, what leads to variable composition of EAF dust. The contents of the main elements vary in a certain range. The example of composition of EAF dust is shown in Table 1.

Table 1 The example of composition of EAF dust [2] Element Content [%] Element Content [%] Zn 2-35 Al 0.0-1 Fe 30-45 Mg 0.1-3 Pb 0.5-2 Na 0.1-1 Cd 0.1-0.3 Si 0.1-2 Ca 1-7 Cl 0.5-3 Cu 0.01-0.2 F 0.05-0.1

EAF dust is, due the content of heavy metals (Table 1), classified as hazardous waste (according to European legislative). Due to the interesting content of zinc it is also potential secondary raw material for production of zinc and /or its compounds.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 143

There are three possible ways of processing EAF dust: hydrometallurgical, pyrometallurgical and combined [1]. Pyrometallurgical methods of processing steelmaking dust require high temperature and reduction agent, whereby product is crude zinc oxide of low commercial value. By hydrometallurgical methods, zinc can be recovered at lower energy consumption by various procedures [2]. The main part of hydrometallurgical treatment includes a purification of solution after leaching in order to decrease concentration of ineligible elements to the level of allowable limits (Tab.2), which do not cause problems in the further electrolytical recovery of zinc. Impurities present in the unpurified neutral solution coming from iron precipitation step, can lead to: lower current efficiency of zinc electrolysis, deposition of impurities on the cathode together with zinc, reverse reaction on the cathode and anode.

Table 2 The example of suitable composition of electrolyte before electrolysis [mg.l-1][4] Zn Cu Cd Co Ni As Sb Ge Fe 140- 170 < 0.2 < 1.0 < 1.0 < 1.0 < 0.24 < 0.3 < 0.05 < 20

Basically, following purification processes can be applied in order to remove ipurities from a solution: chemical precipitation, electrochemical deposition, ion exchange, cementation with zinc powder and solvent extraction. In industrial practice, mainly cementation with zinc powder in a continuous multi-step proces, is used for purification of solutions [3]. The aim of this paper is to study purification of sulphate and chloride solutions coming from leaching of steelmaking dust. The attention was paid to removal of cadmium, lead and iron from the solution and comparison of conditions, at which the process reaches the highest efficiency.

2 Theoretical part Cementation belongs to physico- chemical methods of extracting the metals from a solution, based on the electrochemical reaction between the cementing metal and the ion of the precipitated metal. Thermodynamic feasibility of cementation is determined from the ratio of the values of the electrode potential. The electrode potential of the displacing metal EM must be more negative than that of the displaced metal EMe (EM < EMe). The cementation of the metal is accompanied obviously by a change of its concentration in the solution, and consequently, of its potential.

When the equilibrium values are reached (EM=EMe), the process stops. On the basis of the difference in the electrode potentials, it can be determined the electrode pairs of the cementing and cemented metal [5]. The cementation process can be described by the equation (1) [5]:

n1+ 0 0 n2+ n2Me + n1M = n2Me + n1M (1)

n1, n2- ion charge; Me- cementated metal; M – cementing metal (element) Cementation is heterogenous process between the solid and the liquid phase. On the surface of the reducing metal is fomrmed a stationary layer of the solution- Nernst layer [6-8]. Whereas, cementation is preferred environmental and economic refining operations, several results of metal cementation from the solutions have been published in the literature. The review

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 144 of conditions, under which the cementation was carried out is included in the Table 3. Some of these works deal with the cementation from the synthetic solutions [7-10] and some deal with cementation from a solution after leaching of steelmaking dust [11-12].

Table 3 The review of works and conditions of Cd and Pb cementation Cemented Cementing Temperature pH Solution Literature metal metal [°C]

CdSO4 Cd Zn metal 25-30 5.2 [9]

CdSO4 Cd Zn dust 15 a 45 5.7-6 [10]

ZnSO4 Cd Zn dust 25 a 45 - [11]

ZnSO4 Cd Zn dust 20 5.2-5.4 [12] NaOH Pb, Cd Zn dust 20 8-10 [13] NaOH Pb, Cd Zn dust - 10 [14]

From this review, it is clear, that cadmium and lead cementation was carried out in both acidic and alkaline media, where zinc dust was used as cementing metal in the most of the experiments. It also follows from the literature review, that cementation was realized at temperatures in the range of 25- 45 °C, from pH 5.2 to 6. This work provides a comparison of purification sulphate and chloride solution by cementation from impurities (Cd, Pb, Fe), which can cause problems in zinc electrowinning process. This work deals also with a phase analysis of solid residues formed during cementation.

3 Experimental part 3.1. Material and methods For experimental studies of cementation process, solutions coming from leaching steelmaking dust in sulfuric and hydrochloric acid were used. Before starting experiments these solutions were analyzed by AAS (atomic absorption spectrometry) for concentration of Cd, Pb, Fe and Zn. The concentration of analyzed metals are shown in the Table 4. In this table, also values of pH before cementation are given. Both solutions (sulphate and chloride) were used for studying the cementation. Contents of Cd, Pb, Fe and Zn were analyzed in this solutions. The influence of temperature and pH on cementation efficiency was monitored in these experiments. Following experimental conditions were choosen: time of the experiments 60 minutes, temperatures 25, 50 and 80 °C, 0.5g of zinc powder (purity of 99.99 %) added into 250 ml of the solution. All the experiments were realized in the glass reactor. This reactor was placed into a termostatically controled water bath (Fig. 1). The solution was stirred by glass propeller with constant speed (300 rpm) during all experiments. For adjusting the pH values to 4,5 and 6 the solution of 6M NaOH was used. The pH was adjusted before starting a cementation. Also experiments at temperature 50 °C for 60 minutes, without adjusting pH was carried out in order to compare the cementation efficiency. After experiments, a solution was filtered. Liquid samples (volume of 15 ml) were taken after filtration. These samples were analyzed by AAS (atomic absorption spectrometry Varian AA240+) for concentration of Cd, Pb, Fe and Zn. The resulting filter cake was washed by distilled water to the neutral pH and dried at temperature 80 °C per 24 hours. After drying, the filter cake was weighted and analyzed by XRD diffraction phase analysis with diffractometer Panalytical X-Pert Pro.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 145

Concentrations of monitored metals in the solutions after cementation were compared with the concentrations of metals in the solutions before cementation and the results are shown in Fig. 2 - 9. Efficiency of the cementation and purity of the solution were monitored parameters after cementation.

Table 4 Concentration of metals and pH in solutions before cementation Concentration of metals [mg.l-1] Medium pH Cd Pb Fe Zn H2SO4 18.9 5.1 3308.8 5310 0.64 HCl 13 302.4 1835.2 4570 0.81

Fig. 1 Apparaturs used for the cementation: 1- mechanical stirrer, 2- propeller, 3- pulp, 4- sampler, 5- thermometer, 6- feeder, 7- water thermostat, 8- cementing metal (Zn dust) [1]

4 Results and discussion 4.1 Cementation from sulphate solutions Efficiency of cadmium and lead removal by cementation from sulphate solution at different temperature and pH are shown in Fig. 2. From the results, it is clear that cadmium is removed from the sulphate solution at pH 4, 5 and 6 at all temperatures (Fig. 2a). According to the E – pH diagram of Cd-S-H2O system (Fig. 3a), cadmium is in the solution in the form of Cd2+ at temperatures 25, 50 and 80 °C at pH 4, 5 and 6. Phase analysis (Table 6) confirmed the presence of cadmium in the solid residue after cementation at pH 4 and 5 and temperature 25, 50 and 80 °C. It follows from Fig. 2 that pH value about 1 leads to lower efficiency of removal cadmium comparing to higher value of pH (pH > 4). This was also confirmed by another literature where pH value higher than 1.5 is required for cementation of cadmium from a solution [15]. At cementation of lead (Fig. 2b) the highest efficiency, 87.61 % at temperature 80 °C and pH = 6 was achieved. The lowest efficiency of lead cementation (39.6 %) was achieved at 25 °C and pH = 4. It is clean, from Fig. 2b that efficiency of lead cementation raises with increasing pH. Table 5 shows calculated ΔG°T of the cementation of cadmium and lead from sulphate solution at temperatures 25, 50 and 80 °C. Calculation have been performed by use of program HSC 6.1. The reactions (2 and 3) have tendency to proceed spontaneously in direction of products formation.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 146

Table 5 Calculated ΔG°T of the cementation of kadmium and lead from sulphate solution at temperatures 25, 50 and 80 °C. ΔG° [kJ] Reaction T 25 50 80 (2 ) CdSO4 + Zn = ZnSO4 + Cd -45.952 -45.908 -45.983 (3) PbSO4+Zn=ZnSO4+Pb -55.711 -55.353 -54.956

120 100

100 80

80 60 60 40 40

20 20

Efficiency of lead cementation [%]

Efficiency of cadmium cementation [%] 0 0

25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6 25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6

50 °C; No pH adjustment 50 °C; No pH adjustment Conditions of the experiment Conditions of the experiment

a.) b.) Fig. 2 Cementation efficiency from sulphate solution a.) cadmium ; b.) lead

Eh (Volts) Cd - S - H2O - System at 25.00, 50.00 and 80.00 C 2.0 Eh (Volts) Pb - S - H2O - System at 25.00 C 2.0 PbO2 1.5 1.5 CdO Cd(+2a) 25 1.0 50 80 Cd(OH)2 25 1.0 8050 Pb4(OH)4(+4a) 0.5 0.5 Pb(+2a) PbSO4 CdSO4*2.67H2O25 2PbO*PbSO4 Pb12O17 25 25 PbO*PbSO4 25 25 0.0 255080 50 25 258050 25 3PbO*PbSO4 8050 0.0 Pb4(OH)4(+4a) Pb6(OH)8(+4a)

5025 2550 -0.5 80 80 Pb(HS)3(-a) PbO CdS -0.5 PbS Pb

-1.0 80 50 25 25 -1.0 80 50

-1.5 Cd Pb -1.5

-2.0 0 2 4 6 8 10 12 14 -2.0 0 2 4 6 8 10 12 14 E:\HSC6\EpH\CdS25.iep pH :\HSC6\EpH\CdS25.iepp E:\HSC6\EpH\PbS25.iep pH \HSC6\EpH\CdS25.ieppp :\HSC6\EpH\PbS25.iepp HSC6\EpH\CdS25.iepppp \HSC6\EpH\PbS25.ieppp SC6\EpH\CdS25.ieppppp a.) HSC6\EpH\PbS25.iepppp b.) C6\EpH\CdS25.iepppppp SC6\EpH\PbS25.ieppppp 6\EpH\CdS25.ieppppppp C6\EpH\PbS25.iepppppp Fig. \EpH\CdS25.iepppppppp3 Combined E-pH diagrams of the systems a.)6\EpH\PbS25.ieppppppp Cd-S-H2O and b.) Pb-S-H2O at EpH\CdS25.ieppppppppp \EpH\PbS25.iepppppppp pH\CdS25.iepppppppppp EpH\PbS25.ieppppppppp H\CdS25.ieptemperatures 25, 50 a 80 °C. pH\PbS25.iepppppppppp H\PbS25.iep

Fig. 4a show the efficiency of iron removal from sulphate solution. It can be seen from E – pH diagram of the Fe-S-H2O system, that when pH is adjusted by adding NaOH solution, iron starts to precipitate as iron hydroxide before cementation at all studied temperatures. Phase analysis of

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 147

filter cake after cementation (Table 6) confirmed the presence of iron in the form of Fe2O3 and FeO(OH). At the experiment without adjusting pH at 50 °C, iron was only partially precipitated, i.e. there is still iron remaining in the solution after cementation.

Eh (Volts) Fe - S - H2O - System at 25.00, 50.00 and 80.00 C 120 2.0

1.5 FeO*OH 80 100 25Fe(+3a)50 Fe2O3

1.0 5080 25 80 25 8050 25 50 0.5 80 25 Fe(+2a) 50 60 25 0.0 5080 80 Fe2S3 508025 80 50 25 255080 805025 25 255080 25 8050 -0.5 Fe0.877S 8050 40 25 Fe3O4 8050 25 80 50 -1.0 50 25 20 80 Fe -1.5

Efficiency of purification from iron [%] 0 -2.0 0 2 4 6 8 10 12 14 E:\HSC6\EpH\FeS25.iep :\HSC6\EpH\FeS25.iepp 25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6 \HSC6\EpH\FeS25.ieppp HSC6\EpH\FeS25.iepppp SC6\EpH\FeS25.ieppppp C6\EpH\FeS25.iepppppp 6\EpH\FeS25.ieppppppp 50 °C; No pH adjustment \EpH\FeS25.iepppppppp EpH\FeS25.ieppppppppp pH\FeS25.iepppppppppp Conditions of the experiment H\FeS25.iep

a.) b.)

Fig. 4 a) Efficiency of iron removal from sulphate solution b) E-pH diagram of the Fe-S- H2O system at temperatures 25, 50 and 80 °C

Fig. 5a graphically shows a comparison of zinc content in the sulphate solution before and after cementation at selected conditions. Adding of zinc powder as cementing metal into the solution led to incresing its concentration at all selected temperatures and at pH = 4 and 5. However, at pH = 6 part of zinc, present in the solution, precipitated as it is evident in Fig. 4b what caused lower concentration of zinc in the solution after cementation in comparison to zinc concentration before cementation.

Fig. 5b shows E – pH diagram of the Zn-S-H2O system at temperatures 25, 50 and 80 °C. From Fig. 5b it can be seen, that zinc starts to precipitate from the solution at pH = 6. At pH lower than 6 zinc remains in the solution in the form of Zn2+.

Precipitation of zinc was confirmed by phase analysis, where phases ZnO and Zn(OH)2 was identified in solid residue coming from cementation carried out at pH = 6 and 80 °C (Table 6).

Table 6 Phase composition of selected solid residues after cementation from sulphate solution Conditions of the Phases experiment Temperature Zn(OH) FeO(OH pH Cd CdO Pb Zn ZnO Fe2O3 [°C] 2 ) 25 5 + + + + + + + + 50 5 - + - + + + + + 80 4 + + + + + + - + 80 6 + - + + + + + +

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 148

1.8 Eh (Volts) Zn - S - H2O - System at 25.00, 50.00 and 80.00 C 2.0 1.6 before experiment after experiment 1.5 1.4 50 25 1.0 Zn(+2a) 80 ZnO 25 1.2 8050 1.0 0.5

25 50 0.0 0.8 255080 80 50 25 805025 50 80 25 50 80 25 8050 25 0.6 -0.5 8050 Zn(HS)3(-a) 80 50 25 0.4 -1.0 ZnS

805025 0.2 80 50 25

Content of zinc in the solution [g] 25 -1.5 80 50 0.0 Zn -2.0 0 2 4 6 8 10 12 14 E:\HSC6\EpH\ZnS25.iep pH :\HSC6\EpH\ZnS25.iepp 25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6 \HSC6\EpH\ZnS25.ieppp HSC6\EpH\ZnS25.iepppp SC6\EpH\ZnS25.ieppppp C6\EpH\ZnS25.iepppppp 6\EpH\ZnS25.ieppppppp 50 °C; No pH adjustment \EpH\ZnS25.iepppppppp EpH\ZnS25.ieppppppppp pH\ZnS25.iepppppppppp Conditions of the experiment H\ZnS25.iep a.) b.) Fig. 5 a.) Content of zinc in the sulphate solution before and after cementation b.) E-pH

diagrams of the Zn-S-H2O system at temperatures 25, 50 a 80°C

4.2 Cementation from chloride solution Efficiencies of cadmium cementation in chloride solution are ilustrated in Fig. 6a. These results show that cadmium cementation from chloride solution reached 100 %. It means, that cadmium in chloride solution (as in the case of sulphate solution) was completely cemented without any influence of temperature and pH. Fig. 7a shows a combined E-pH diagram of the Cd-Cl-H2O system at temperatures 25, 50 and 80 °C. According to this diagram, cadmium is in the region of water stability in the form of CdCl3(-a) at studied conditions. In the case of experiments without pH adjusting, cemetation efficiencies of cadmium and lead were very low, 19.1 % and 4.28 % respectively. Thermodynamic study of cadmium and lead cementation from chloride solution at temperatures 25, 50 and 80 °C is listed in Table 7. It results from thermodynamic study that the reactions will proceed in the direction of product formation at all studied temperatures.

Table 7 Calculated ΔG°T of the cementation of cadmium and lead from the chloride solution at temperatures 25, 50 and 80 °C

ΔG° [kJ] Reaction T 25 50 80 (4) CdCl2+Zn= ZnCl2 +H2 -36.224 -26.337 -26.558 (5) PbCl2 + Zn= Pb + ZnCl2 -56.204 -56.167 -56.111

Efficiencies of lead cementation in chloride solution are illustrated in Fig. 6b. The highest efficiency of lead cementation, 99.94 %, was achieved at pH = 6 and temeperature 50 °C. Fig. 7 shows a combined E-pH diagram of the Pb-Cl-H2O system at temperatures 25, 50 and 80 °C. It results from the E-pH diagram, that lead is in the region of water stability in the form of

PbCl4(-a) at all studied temperatures.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 149

As can be seen from achieved efficiencies, in chloride solution unlike sulphate solution, 100 % cementation of efficiencies were reached at all studied conditions. Achieving higher cementation efficiency in the sulphate solution was probably inhibited by formation of PbSO4.

120 120

100 100

80 80

60 60

40 40

20 20

Efficiency of the lead cementation [%]

Efficiency of cadmium cementation [%] 0 0

50 °C; No pH adjustment 50 °C; No pH adjustment Conditions of the experiment Conditions of the experiment

a.) b.) Fig. 6 Cementation efficiency from chloride solution: a.) cadmium; b.) lead

Eh (Volts) Cd - Cl - H2O - System at 25.00, 50.00 and 80.00 C Eh (Volts) Pb - Cl - H2O - System at 25.00, 50.00 and 80.00 C 2.0 2.0 Cd(+2a) CdO PbO2 Pb(+2a) 1.5 802550 Cd(OH)2 1.5 5080

2550CdCl(+a)80 508025 25505025 25 1.0 80 8050 1.0 2550 25 80 5025 8050 80 25 80 50 0.5 CdCl3(-a) 0.5 PbCl4(-a) 50 25 80 Pb12O175025 508025 CdOHCl 80 50 25 80 25 50 25 80 50 25 80 80 50 25 0.0 0.0 8050 PbCl2 Pb3Cl2O2 80 50 25 PbO 805025 805025 80 50 25 5025 5025 -0.5 508025 80 -0.5 80 25 80 5025 80 50 25 80 50 -1.0 -1.0 Pb Cd -1.5 -1.5

-2.0 -2.0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 E:\HSC6\EpH\CdCl25.iep pH E:\HSC6\EpH\PbCl25.iep pH :\HSC6\EpH\CdCl25.iepp :\HSC6\EpH\PbCl25.iepp \HSC6\EpH\CdCl25.ieppp \HSC6\EpH\PbCl25.ieppp HSC6\EpH\CdCl25.iepppp a.) HSC6\EpH\PbCl25.iepppp b.) SC6\EpH\CdCl25.ieppppp SC6\EpH\PbCl25.ieppppp C6\EpH\CdCl25.iepppppp C6\EpH\PbCl25.iepppppp 6\EpH\CdCl25.ieppppppp 6\EpH\PbCl25.ieppppppp \EpH\CdCl25.iepppppppp \EpH\PbCl25.iepppppppp EpH\CdCl25.ieppppppppp EpH\PbCl25.ieppppppppp Fig.pH\CdCl25.iepppppppppp 7 Combined E-pH diagrams of the systemspH\PbCl25.iepppppppppp a.) Cd-Cl-H2O , b.) Pb-Cl-H2O at H\CdCl25.ieppppppppppp H\PbCl25.ieppppppppppp \CdCl25.iep temperature 25, 50 and 80 °C \PbCl25.iep

Efficiencies of iron cementation from chloride solution is illustrated in Fig. 8a. As it results from combined E-pH diagram of the Fe-Cl-H2O system at temperatures 25, 50 and 80 °C (Fig. - 8b), iron is present in the chloride solution in the form of FeCl2 to pH = 5. At pH > 5, iron starts to precipitate. Efficiency of iron cementation at pH = 4 was 96 % at all selected temperatures. Iron was precipitated from the solution by adjusting the pH solution to values 5 and 6 by adding a hydroxide sodium solution. XRD phase analysis confirmed the presence of iron in the form of FeO(OH) in the solid residue after filtration (Table 8).

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 150

In the case of the experiment without adjusting pH (pH about 1) iron was cemented with lower efficiency (13.13 %) comparing to higher values of pH.

Eh (Volts) Fe - Cl - H2O - System at 25.00, 50.00 and 80.00 C 2.0 120 Fe(+3a) Fe2O3 255080 FeO*OH 1.5 255080 100 805025 1.0 25 8050 FeCl2(+a) 80 0.5 805025

0.0 60 805025 805025 805025 25 FeCl(+a)Fe(+2a) 25 8050 -0.5 805025 25 8050 Fe3O4 25 40 8050 Fe(OH)2 -1.0

Fe 20 -1.5

-2.0

Efficiency of purification from iron [%] 0 0 2 4 6 8 10 12 14 E:\HSC6\EpH\FeCl25.iep pH :\HSC6\EpH\FeCl25.iepp \HSC6\EpH\FeCl25.ieppp HSC6\EpH\FeCl25.iepppp 25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6 SC6\EpH\FeCl25.ieppppp C6\EpH\FeCl25.iepppppp 6\EpH\FeCl25.ieppppppp \EpH\FeCl25.iepppppppp EpH\FeCl25.ieppppppppp pH\FeCl25.iepppppppppp 50 °C; No pH adjustment H\FeCl25.ieppppppppppp \FeCl25.iep Conditions of the experiment

a.) b.) Fig. 8 a.) Efficiency of iron removal from chloride solution b.) E-pH diagram of the Fe-Cl-

H2O system at temperatures 25, 50 a 80 °C

1.4 Eh (Volts) Zn - Cl - H2O - System at 25.00, 50.00 and 80.00 C 2.0 before experiment 1.2 Zn(+2a) ZnO after experiment 1.5 80 50 25

805025 1.0 1.0 805025 25 8050 0.5 0.8 ZnCl(+a)

25 5080 0.0 0.6

25 -0.5 8050 0.4 255080

-1.0 2550 80 0.2 -1.5 Content of zinc in the solution [g] Zn 0.0 -2.0 0 2 4 6 8 10 12 14 E:\HSC6\EpH\ZnCl25.iep pH :\HSC6\EpH\ZnCl25.iepp \HSC6\EpH\ZnCl25.ieppp 25 °C; pH=425 °C; pH=525 °C; pH=650 °C; pH=450 °C; pH=550 °C; pH=680 °C; pH=480 °C; pH=580 °C; pH=6 HSC6\EpH\ZnCl25.iepppp SC6\EpH\ZnCl25.ieppppp C6\EpH\ZnCl25.iepppppp 6\EpH\ZnCl25.ieppppppp \EpH\ZnCl25.iepppppppp 50 °C; No pH adjustment EpH\ZnCl25.ieppppppppp pH\ZnCl25.iepppppppppp H\ZnCl25.ieppppppppppp Conditions of the experiment \ZnCl25.iep a.) b.) Fig. 9 a.) Content of zinc in the chloride solution before and after cementation

b.) E-pH diagram of the Zn-Cl-H2O system at temperatures 25, 50 a 80 °C

Fig. 9a graphically shows comparison of zinc content in the chloride solution before and after cementation at selected conditions. It results from Fig. 9a, that using zinc as cementing metal

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 151 increases its concentration in the solution at pH = 4 and 5 and at all studied temperatures. Similarly, as in the case of sulphate solution, zinc starts to precipitate at pH = 6.

This fact is confirmed by E-pH diagram of the Zn-S-H2O system at 25, 50 and 80 °C, where zinc is in the soluble form till pH = 6, but over this value zinc starts to precipitate. Phase analysis of the solid residue after cementation confirmed the presence of phases ZnO and Zn(OH)2 (Table 6). In the case of the experiment without adjusting pH, zinc concentration raised too, what could be casued by its dissolution due to the presence of free acid in the solution.

Table 8 Phase composition of selected solid residues after cementation from chloride solution Conditions of the Phases experiment Temperatur pH Cd CdO Pb Zn ZnO Zn(OH) NaCl FeO(OH) e [°C] 2 25 6 - - + + - + + + 50 6 + + + + + + + + 80 4 + + + + + + + -

Experimetal results show the possibility of using cementation as way of removing metals (mainly Cd, Pb and Fe) from solutions to the acceptable limits. The most effective conditions of cementation found out in this work are listed in Table 9. However, it is obvious that at pH 6 except of cementation occure also precipitation, what contribute to improvement overall refining process.

Table 9 The most effective conditions of cementation Cd, Pb and Fe Metals Cd Pb Fe Concentration [mg.l-1] Medium/ most efective Befor Befor After After Before After conditions e e Sulphate solution / pH 6; 80 18.9 0 5.1 9 x10-5 3.31 6 x10-3 °C Chloride solution / pH 6; 50 13 0 0.3 4.4 x10-5 1.84 1.8 x10-4 °C 5 Conclusion From experimental study of cadmium and lead cementation from solutions coming from leaching of steelmaking dust, following conclusions can be stated: Cementation of cadmium was carried out under selected conditions (pH = 4, 5 and 6 and at temperatures 25, 50 and 80 °C) with 100 % efficiency in both sulphate and chloride solution. Cadmium was completely cemented at all selected conditions without any influence of temperature and pH. Phase analysis of solid residue after cementation confirmed the presence of cadmium as Cd and CdO, which probably formed by oxidation of Cd in solid residue. The highest efficiency of lead cementation in suplhate solution, 87.61 %, was reached at pH = 6 and temperature 80 °C. In chloride solution the efficiency of 99.94 % was achieved at pH 6 and 80 °C. Lead was present in solid residues in the form of Pb in both suplhate and chloride solution, what confirmes its cementation.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 152

Phase analysis of solid residues after cementation confirmed, that iron precipitates from sulphate solution by increasing pH above 4 as Fe2O3 and FeO(OH). Adjusting pH to the value of 6 casued partial precipitation of zinc from suphate solution. Phase analysis of solid resiue confirmed its presence in the form of Zn, ZnO and Zn(OH)2. The same phases were identified also in solid residues coming from chloride solution. It results from comparison of experiments with and without adjusting pH in both sulphate and chloride solutions, that increasing pH value has a positive effect on efficiency of cementation cadmium and lead from the solution. However, adjusting pH to the value of 6 causes precipitation of iron and partial precipitation of zinc, which stays in solid residues.

References [1] T. Havlík, B.Vidor e Souza, M. Brnardes, I. Schneider, A. Miškufová: Acta Metallurgica Slovaca, Vol. 12, 2006, No.1, p. 42- 53 [2] G. Graf: Zinc, Ullmann´s Encyklopedia of Industrial Chemistry, first ed., Wiley- VCH Verlag GmbH a Co., 2005 [3] Z. Sedláková, D. Oráč, T. Havlík: Acta Metallurgica Slovaca, Vol. 12, 2006, No.1, p. 338 - 345 [4] M. Wua, J.H. She, M. Nakano: Engineering Applications of Artificial Intelligence, Vol.14, 2001, No.5, p. 589–598, doi: 10.1016/S0952-1976(01)00019-7 [5] T. Havlík: Hydrometallurgy, Principles and application, first ed., Košice: Emilena, 2005, ISBN 80-8073-337-6 [6] M. Štofko, M. Štofková: Non-ferrous metals, first. ed., Košice: Emilena 2000, ISBN 80- 7099-527-0 [7] R. Lacko, M. Štofko, M. Škrobian: Activation cementation of metal by current pulse, Waste recycling, VŠB-TU, Ostrava, 2007, p. 191- 196 [8] R. Lacko, J. Kaduková: Proceedings of the workshop held on the occasion of the anniversary of prof. Štofko, Herľany, EQULIBRIA, 2008, p. 61-66 [9] N.K. Amin, Z. El-Ashtoukhy, O. Abdelwaha: Hydrometallurgy, Vol. 89, 2007, No.3, p. 224–232, doi: 10.1016/j.hydromet.2007.07.007 [10] M. Aurousseau, N.T. Pham, P. Ozil: Ultrasonics Sonochemistry, Vol. 11, 2004, No. 1, p. 23–26, doi: 10.1016/S1350-4177(03)00130-5 [11] M. S. Safarzadeh, D.Moradkhani, M. Ilkhchi: Chemical Engineering and Processing, Vol. 46, 2007, No.12, p. 1332–1340, doi: 10.1016/j.cep.2006.10.014 [12] S.R. Younesi, H. Alimadadi, E. Alamdari: Hydrometallurgy, Vol. 84, 2006, No.3-4, p. 155- 164, doi: 10.1016/j.hydromet.2006.05.005 [13] O. Ruiz, C. Clemente, M. Alonso, F.J Alguancil: Journal of Hzardous materials, Vol. 141, 2007, No.1, p. 33-36, doi: 10.1016/j.hazmat.2006.06.079 [14] G.Orhan: Hydrometallurgy, Vol. 78, 2005, No. 3, p. 236–245, doi: 10.1016/j.hydromet.2005.03.002 [15] R. Ligiane: Minerals Engineering, Vol. 20, 2007, No. 9, p. 956-958, doi:10.1016/j.mineng.2007.04.016

Acknowledgements This work was supported by Ministry of Education of the Slovak Republic under grant MŠ SR 1/0293/14. Article is the result of the Project implementation: University Science Park

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156 Acta Metallurgica Slovaca, Vol. 21, 2015, No. 2, p. 142-153 153

TECHNICOM for Innovation Applications Supported by Knowledge Technology, ITMS: 26220220182, supported by the Research & Development Operational Programme funded by the ERDF.

DOI 10.12776/ams.v21i2.451 p-ISSN 1335-1532 e-ISSN 1338-1156