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Page 1: Decontamination as important step towards recycling

Resources, Conservation and Recycling, 10 (1994) 107-116 107 Elsevier Science B.V.

Decontamination as important step towards recycling

I. Gaballah a, N. Menad a, D. Hartmann b, G. Lyaudet b and P. Michel b aMineral Processing and Environmental Engineering Team, LEM, CNRS UA 235, Vandtruvre,

France bCompagnie Gbn&ale de Matibres Nuclbaires "'COGEMA"- SIMO & SEPA, Bessines, France

ABSTRACT

Non ferrous metallurgy generates different kinds of wastes from the hydro- and/or pyrometallurgy. These residues contain up to 25% of valuable metals but also contain elements such as As, Hg, Cd, Se, etc. In most cases, these residues are hazardous wastes and dangerous for the environment. The de- contamination of these residues is indispensable before their recycling in the classical metallurgical plants. The objective of this paper is to describe preliminary results of thermal treatments under con- trolled atmospheres for the decontamination of these residues. The elimination rates of arsenic in function of these treatments are reported.

INTRODUCTION

The public opinion pressure, the increase of waste disposal costs, the ele- vation of the environment regulation's level, the low metal market, the release of the strategic metal stock of the Eastern European countries, ... causes some EC enterprises to lose market shares and competitiveness. These enterprises will survive if they are capable of undertaking a deep and wide change in the basic concepts for integrated process development including the recycling and/ or the inertization of their wastes. On the other hand, the decontamination and recycling of industrial secondary products and wastes is emerging as a new industry. The opening of European subsidiaries of foreign companies and major investment in this field has to be considered as a confirmation of the importance of this industry to the EC countries.

The problem of industrial wastes and by-products can be treated on three different levels: I. decontamination of these residues so as to be recycled or inertized,

Correspondence to: I. Gaballah, Mineral Processing and Environmental Engineering Team, LEM, CNRS UA 235, INPL, BP 40, 54501 Vandoeuvre, France.

0921-3449/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved.

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108 I. GABALLAH ET AL.

2. modification of the actual flow-sheet for the partial integration of wastes and/or by-products in the manufacturing process,

3. conception ofwasteless process based on almost full integration of the by- products and wastes in the production cycle.

Only the first level will be discussed in this paper. The decontamination of the industrial residues is concerned with two limitations. The first is the spe- cific input of the actual industrial process that had to be matched for the re- cycling of these residues after their treatment. The second is the environmen- tal regulation related to the composition of solids for waste disposal which have to be similar to that of the treated solids.

The earth's crust and igneous rocks contain about 3 mg/kg arsenic. Arse- nopyrite (FeAsS) is the most abundant ore of this element that is also found as arsenolite m s 2 0 3 , mimetite PbsC1 ( A s O 4 ) 3, olivenite C u 2 O H A s O 4 , cobali- tite CoAsS, and proustite AgaAsS3 etc. [ 1 ]. Arsenic oxide is usually produced as a by-product of copper, gold, lead, and nickel extraction industries.

The toxicity of arsenic is historically well known. Arsenic is mobile within the environment and may circulate in various forms through the atmosphere, water and soil. The major sources of arsenic release into the environment are the mining and metal extraction industries, the burning of fossil fuels, pesti- cide use, etc that could amount to about 125000 tons/year [2]. Arsenic con- stitutes a serious drawback for non ferrous metallurgy. The hydrometallurgi- cal treatment of complex sulfide ores generates residues containing up to 25% of arsenic oxides.

The actual French regulations concerning the arsenic content of solids im- pose the treatment for those containing more than 8% of arsenic. Solids hav- ing arsenic content of less than 8% and more than 0.1% could be disposed of

T A B L E 1

Compar i son between the suggested European and actual French s t andards

Element Clark* Suggested European C o m m u n i t i e s French s tandards S tandards ( m g / K g ) ( m g / K g )

Harmless Dangerous Inert Class I Class II waste waste waste

As 3.00 1-2 2 .0-10 .0 < 1 < 10 < 2 . 0 Ni 75.00 < 4 4 .0-20 .0 total < 100 - Cd 0.20 < 1 1.0-5.0 content o f < 50 < 5.0 Cu 55.00 < 20 20 .0 - 100.0 these - < 20.0 Hg 0.08 < 0 . 2 0 .2-1 .0 e lements < 10 < 0 . 2 Pb 12.50 < 4 4 .0-20 .0 mus t be < 100 < 30.0 Zn 70.00 < 20 20 .0-100 .0 < 50 < 500 -

Clark*: def ines the e l emen t ' s abundance in the ear th ' s crust ( m g / K g ) .

Page 3: Decontamination as important step towards recycling

DECONTAMINATION AS AN IMPORTANT STEP TOWARDS RECYCLING 109

in salt mines. Table 1 summarizes the suggested EC and the actual French standards defining the composition of the lixiviation test of solid residues [31.

This paper describes the effect of thermal treatments, at different temper- atures and under various controlled atmospheres, on the physicochemical transformations of hydrometallurgical wastes. Attention will be focalized on arsenic elimination from these samples.

BIBLIOGRAPHY

The main process used for the elimination of arsenic from hydrometallurg- ical waste solutions is the precipitation as ferric and/or calcium arsenates. However, this operation produces compounds that may be unstable and toxic. Calcium arsenate is stable in alkaline media, however in presence of atmos- pheric CO2, it decomposes leading to the formation of CaCO3 and the liber- ation of arsenic oxide [4-6]. On the other hand, the stoichiometric ferric arsenate exhibits unacceptably high solubility [ 7 ]. Limited solubility of this compound is obtained when the Fe/As ratio was higher than 2 [8]. Robins and Tozawa [7] suggested that the apparent low solubility of calcium and ferric arsenates may be attributed to the presence of impurities such as Cd, Cu, Ni, Pb and Zn. Harris and Monette [ 9 ] confirmed that basic ferric arse- nates, with a Fe/As molar ratio >_ 4, give arsenic solubility 100 to 1000 times lower over a pH range of 3 to 7.

Removal of arsenic during the pyrometallurgical processing of sulfides, us- ing air or enriched air, is well known. However, little work is done on the elimination of this element in nitrogen. Such process will lead to the recovery of arsenic as ms2S3 that is less toxic and has a lower solubility (see Table 2). Kusik [ 10 ] experimented the removal of arsenic compounds from sulfide copper concentrates under a nitrogen and carbon dioxide atmospheres. At 600 °C, he obtained arsenic sulfide with a calculated recovery rate of about 93%.

Another possibility for arsenic removal is the chlorination of arsenic com- pounds to produce arsenic chloride that could be reduced by hydrogen to ar- senic (Eqs. ( 1 ) and (2) ).

m s 2 0 3 +6 HC1--,2 AsC13 +3 H 2 0 ( 1 )

TABLE 2

Solubility of some arsenic compounds expressed as g/100 ml of water [ 9 ]

Temperature °C As203 As205 As2S3 As2S5 AsH3

0-20 1.21 59.5 0.008 0.00136 0.15

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1 10 I. GABALLAH El" AL.

2 AsC13 + 3 H 2 --* 1/2 As4 + 6 HC1 (2)

Ivashentsev and Kutakova [ 10 ] chlorinated arsenic oxide with HC1 and NH4C1 in the temperature range of 100 to 250°C. They confirmed the feasi- bility of Eqs. (1) and (2) and found that the apparent activation energy of the reaction was 4.1 kcal/mole. Toyabe et al. [ 12 ] reported that Sumitomo Metal Mining Co. produces high purity arsenic metal for semiconductors. The process consists of purification of arsenic oxide obtained from the sulfide smelters followed by chlorination of As203. AsC13 is purified by simple and fractional distillation then reduced by hydrogen followed by the purification of the arsenic metal by sublimation.

It should be underlined that all the reported research work confirms that the total removal of As compounds from sulfide concentrates, industrial by- products and wastes was impossible.

Experimental method and apparatus The decontamination of three different samples of by-product and waste of

the non-ferrous hydrometallurgical processing is examined. Their arsenic content varies from 0.5 to 21.7% and significant concentration of mercury and selenium are present in the first sample. The total Cu, Pb and Zn contents of these three samples are 24, 23 and 14%, respectively. Table 3 summarizes the composition of these samples.

Thermogravimetric analysis of these samples is realized in presence of air, chlorine, and hydrogen. Isothermal treatment of the solids is performed with the same gases mentioned above between 200-800°C. The treated residues and the condensates were examined by X-Ray Diffraction (XRD) and Scan- ning Electron Microscope (SEM). The residues were analyzed by classical chemical analysis. The apparatus used in this study are described in refer- ences [ 13,14].

Using the above-mentioned gas mixtures, the reaction products could be AsC13, ASH3, As203 and As °. The evolution of their vapor pressures in func- tion of temperature is illustrated in Fig. 1. As could be expected, arsenic hal- ides have a boiling point lower than that of the oxides and metallic arsenic.

TABLE 3

Chemical composition and specific surface

S \ % As Pb Hg Cd Zn Cu Sb Se Ca Fe Stot H20 Sp.S. m2/g

1 0.5 15.9 3.2 0.06 0.1 8.2 3.34 0.03 0.04 11.5 44.4 8.674-0.01 2 21.7 4.8 0.6 0.80 16.0 2.0 0.12 0.20 0.10 1.00 22.9 51.0 34.45+1.15 3 13.9 4.3 0.6 0.04 3.2 6.3 0.45 14.00 10.6 18.3 2.84+_0.06

Page 5: Decontamination as important step towards recycling

DECONTAMINATION AS AN IMPORTANT STEP TOWARDS RECYCLING 111

800 ~ = :

,oo I I I I E 111l

:" l l l l IO 300

t~ ' 200 >

,oo /7 l ," /- ~ l : ' J

- 0 0 0 * 1 0 0 0 100

I I l I

! /

/ / /

J ! _ , t _. . . . , /" j

600 700 200 300 400 500

Temperature *C

Fig. 1. Vapor pressure of some arsenic compounds.

TABLE4

Results of XRD and SEM analysis

Sample XRD Crystallized compounds

Scanning Electron Microscope

Major elements Minor elements

1 PbSO4, Cu2.xSe, SiO2 S, Pb, Cu Se, O, Hg, Si, Fe, Zn 2 As203, ZnS, PbS S, Pb, Zn, As, Cu Fe, Cd, Si, Ca, O 3 CuFeS2, As203, FeS2, PbSO4, SiO2 S, Fe, As, O, Cu, Pb Si, Zn, Ca

The chlorination of these samples may allow a better elimination of arsenic compounds provided they can be converted to AsC13.

Phys&ochemical characterization of the raw samples Samples used in this study are wastes of the hydrometallurgical process ob-

tained by precipitation. Their water content varies from 18 to 51% and their specific surface area is included between 2.8 and 34.5 m2/g (Table 3 ). Some of the precipitated solids are amorphous and/or have a complicated crystal- line structure. However, XRD revealed the presence of oxide, sulfide, sele- nide and sulfate of valuable elements. Arsenic is detected as trioxide. As2S 3 was not detected. The qualitative composition of these samples was deter- mined by SEM. Table 4 groups the information obtained by these two techniques.

Thermogravimetric analysis About 100 mg of dried sample was preheated, in a quartz nacelle, before

the introduction of the gas mixture. The rate of temperature increase was

Page 6: Decontamination as important step towards recycling

112 I. GABALLAH ET AL.

25 °C/min, followed by a plateau at 1000°C and the total reaction time was 2 h. Residues are examined by XRD and SEM.

R E S U L T S

Figure 2 displays the weight loss evolution of the three samples in presence of air, C12 + N2 and H2 as function of the temperature.

As indicated in Tables 3 and 4, the valuable metals content are 24, 23 and 14% for samples 1 to 3 respectively. The treatments done in this work do not affect the lead sulfate. According to Table 3, the C u + Z n contents of these samples are 8, 18 and 9.5 respectively.

The curves of Fig. 2A indicate: 1. the elimination for sample No. 1, at T < 200 ° C, of Hg and Se compounds,

that amounts to ~ 10% and the dehydration of samples No. 2 and 3, 2. at T < 300°C, the arsenic trioxide was volatilized, 3. at T > 500°C, oxidation of sulfides occurs.

Curves of Fig. 2B show that the effect of the chlorinating gas mixture was very important and starts at room temperature. This is illustrated by the in- crease of the sample's weight. Chlorination of copper, zinc and lead was fol- lowed by the volatilization of the metal chlorides.

Fig. 2C shows the effect of hydrogen on the three samples. Dehydration, volatilization and/or reduction of arsenic compounds followed by a partial reduction of metal sulfides.

The thermogravimetric analysis permits the definition of the temperatures for the isothermal treatment of these samples under controlled atmosphere.

Isothermal treatment About 10 g was distributed in a mullite boat. The sample was introduced in

the reactor after the homogenization of its atmosphere. The reaction time was 4 h. The temperature range was 200 to 800°C. Thermal treatments of the samples were performed with three gas mixtures: air, chlorine + nitrogen and hydrogen. At the end of the experiment, the reaction product was quenched. The condensate and the residue were examined by XRD. Only the residue of the thermal treatment was analyzed to determine the harmful elements contents.

Table 5 groups the conditions and the qualitative chemical composition of the reaction products for a selected number of experiments where the re- moval of arsenic was considered successful. Treatment of sample No. 1 in air at 500°C allows the elimination of As, Hg and Se with an extraction rate "z" of 56, 99.96 and 17% respectively (see Table 6 ). The same treatment applied on samples No. 2 and 3 leads to the arsenic extraction of 97.62 and 75.19% respectively. The different As extraction rate from the three samples is prob-

Page 7: Decontamination as important step towards recycling

DECONTAMINATION AS AN IMPORTANT STEP TOWARDS RECYCLING

RESULTS 8O

60 ~

A. Air

t / 1 .

0 0 2 0 0 4 0 0 6 0 0 8 0 0 1000

T e m p e r a t u r e °C

B. Chlorine + N i t r o g e n 100

80

60

3

• -~ 40

2O

-20

80

60

o,

4o

;20

f

0 2 0 0

! / / 1 / ~iiii

1

4 0 0 6 0 0

T e m p e r a t u r e ° C

I ~ ' ~ ' 1

8 0 0 1 0 0 0

C. Hydrogen

f

3

. . . . . . . z 200 4 0 0 6 0 0

T e m p e r a t u r e °C

8 0 0 1 0 0 0

Fig. 2. Thermogravimetric analysis of three samples with different gas mixtures.

113

Page 8: Decontamination as important step towards recycling

114 I. GABALLAH ET AL.

TABLE5

Qualitative chemical analysis of condensate and residue of samples treated at different temperatures with different gas mixtures

S* T°C G.M.** Solid Major elements Minor elements

Raw S, Cu, Pb Se, O, Hg, Si, Fe, Zn 500 air C+ Hg, Se O, As

R + + S, Cu, Pb O, Se, Zn 800 C Hg, Se, As O, Br

R S, Cu, Pb O, Si 400 C12 + N2 C S, O, Hg CI, Se

R C1, S, Cu, Pb O, Si 800 H2 C Hg, As, Br, S Se, O, Pb

R S, Cu, Pb, Se Si, O, Fe

raw S, Zn, As, Pb Cu, Fe, Cd, Si, Ca 500 air C As, S O

R Zn, S Cu, Pb, O, Fe, Ca, Si 400 C12+N2 C As, S, Fe, Zn, C1, O Cu, Se

R Ci, Zn, Pb O, S, Cd, Fe, Cu 400 H2 C As, S O

R S, Zn, Cu, Pb Fe, O, Si

raw S, Fe, As, O, Cu, Pb Si, Zn, Ca 500 air C As, O Hg

R S, Fe, O, Cu, Si, Pb Zn, Ca, As 800 C12 +N2 C S, Fe, Cu, Zn, As, O, Pb C1

R Si, Mg, C1, Ca, O Fe, Pb 600 H2 C As S, O, Hg

R Fe, S, Cu, Si, O Pb, Mg, Ca, Zn

*Sample number, **Gas mixture, +Condensate, + +Residue.

ably related to the initial arsenic content and the nature of the arsenic bearing compounds. Increasing the thermal treatment temperature, for sample No. 1, to 800°C permits the extraction of 90, 99.99 and 98% of the initial As, Hg and Se content. Clearly the thermal treatment in air will not allow the total removal of the arsenic, mercury and selenium of this sample.

Table 6 shows that the chlorination of sample No. 1 at 400 o C permits the elimination of 98.6, 99.99 and 97.1% of As, Hg and Se respectively. Submit- ting sample No. 3 to hydrogen at 600 ° C, decreases the arsenic content from 14% to 0.09% which corresponds to the removal of 99.9% of As. One may mention that the residues of the thermal treatments of the three samples con- tain 17 to 53% of compounds of copper, lead and zinc and less than 500 ppm of arsenic. Such solids could be recycled in classical pyrometallurgical processes.

One may underline that the chemical and crystalline phase composition of these samples are complex due to their hydrometallurgical origin. Their evo-

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DECONTAMINATION AS AN IMPORTANT STEP TOWARDS RECYCLING

TABLE 6

Extraction rate of arsenic, mercury and selenium as function of temperature and gas mixture

115

S Solid Atmo. T°C %W.L. %As %T %Hg % r %Se % z %zto t .

1 Raw 0.500 3.2100 3.34 Residue air 500 25.93 0.300 55.56 0.0020 99.96 3.76 16.62 41.8

air 800 34.50 0.700 90.83 0.0005 99.99 0.09 98.19 96.8 C12-N2 400 31.50 0.030 98.58 0.0020 99.99 0.12 99.07 97.7

Raw 21.700 2 Residue air 500 76.55 2.200 97.62 N.D. N.D. N.D. N.D. 87.1

C12-N2 400 63.73 0.500 99.16 N.D. N.D. N.D. N.D. 94.4

Raw 13.900 3 Residue air 500 40.53 5.800 75.19 N.D. N.D. N.D. N.D. 60.0

H2 600 53.38 0.087 99.90 N.D. N.D. N.D. N.D. 99.1

z %: extraction rate = (Initial M - Final M )* 100/Initial M.

lution during the thermal treatments leads to the formation of new com- pounds, solid solution, etc. which makes difficult their subsequent decontam- ination. Clearly, the thermal treatment with one gas mixture may not be able to fulfill the total decontaminat ion of such kind of samples. Combined and successive thermal treatment of these samples is under investigation.

C O N C L U S I O N S

The decontaminat ion of three samples of hydrometaUurgical residues was examined in this study. These samples contains 14 to 25% of valuable ele- ments such as copper, lead, zinc, etc. They also contain about 10 to 22% of As, Hg, Cd, Se, etc.

Treatment of these samples in air up to 800°C, do not allow the total elim- ination of the toxic elements. Using a mixture of chlorine and nitrogen at low temperature < 400° C, it was possible to chlorinate the toxic elements with an extraction rate higher than 94%. Thermal treatments with hydrogen allow the removal of 99.9% of arsenic.

The residues of the thermal treatments contain about 17 to 53% of valuable elements and less than 500 ppm of toxic elements. Such solids could be recy- cled in classical pyrometallurgical processes. Some of the residue of the ther- mal treatments could be considered, by the actual standards, as inert material.

It should be underlined that full decontamination of such samples will re- quire a successive or combined thermal treatment with different gas mixtures.

Page 10: Decontamination as important step towards recycling

116 I. GABALLAH ET AL.

REFERENCES

1 A. Betekhtin, 1960. Arsenic. In: The Course of Mineralogy. Peace, Moscow. pp. 157-159. 2 L6onard, A., 1991. Arsenic. In: Metals and their compounds in the environment, edited by

E. Merian. VCH, Weinheim, Germany, pp. 751-774. 3 French Ministry of Environment. 4 R.G. Robins, 1981. The solubility of metal arsenates. Metallurg. Trans., B. 12 (B) 103-

109. 5 R.G. Robins, 1983. The stabilities of arsenic (V) and arsenic (III) compounds in aqueous

metal extraction systems. In: K. Osseo-Asare and J. Miller (eds.), Hydrometallurg Reseach Develop. and Plant Practice. The Metallurgical Society ofAIME, Warrendale, Pa, pp 291- 310.

6 R.G. Robins, 1985. The aqueous chemistry of arsenic in relation to hydrometallurgical processes. Impurity Control and Disposal, Proc. 15th Ann. Hydrometallurg. Meet. CIM, Vancouver, pp 1 / 1-1/26.

7 R.G. Robins and K. Tozawa, 1982. Arsenic removal from gold processing waste waters: the potential ineffectiveness of lime. CIM. Bull., 75 (4): 171-174.

8 A. Kontopoulos et al, 1988. Arsenic control in hydrometallurgy by precipitation as ferric arsenate. Proceeding of the first international conference on hydrometallurgy (ICHM 88 ). Edited by Zheng Yulian, Xu Jiazhong, p. 672.

9 E. Krause and V.A. Ettal, 1985. Ferric arsenate compounds: are they Environmentally Safe? Solubilities of basic Ferric Arsenate. Impurity control and Disposal, Proc. 15th Ann. Hy- drometallurg. Meet. CIM, Vancouver, pp 5/1-5/20.

10 C.L. Kusik and R.M. Nadkarni, 1988. Pyrometallurgical Removal of Arsenic from Copper Concentrates. In: R.G. Reddy, J.L. Hendrix and P.B. Quineau (eds.), Proc. Symp. Aresenic Metallurgy Fundamentals and Application, 25-28 January 1988, Phoenix. Metallurgical Society Inc., pp. 337-349.

11 Ya. I. Ivashentsev and L.I. Kutakova, 1968. Reaction of arsenic oxide with ammonium chloride and hydrogen chloride. Izv. Vyssh. Ucheb Zaved. Khim. Tekhnol., 09612,11 (7), 845-847.

12 K. Toyabe, C. Segawa, H. Kadoya and H. Ohwa, 1988. High Purity Arsenic Metal Produc- tion at SMM's Niihama Copper Refinery. In: R.G. Reddy, J.L. Hendrix and P.B. Quineau (eds.), Proc. Symp. Aresenic Metallurgy Fundamentals and Application, 25-28 January 1988, Phoenix. Metallurgical Society Inc., pp. 351-362.

13 I. Gaballah, E. Allain and M.-Ch. Meyer-Joly, 1990. Leaching of tin slag and subsequent chlorination of the Ta and Nb concentrate. In: K.C. Liddell, D. Sadoway and R. Bautista (eds.), Refractory Metals: Extraction, Processing and Applications. TMS, pp. 283-296.

14 I. Gaballah, E. AUain and M. Djona, 1993. Chlorination and carbochlorination of a tan- talum and niobium pentoxides bearing concentrates. TMS Ann. meet., Denver, EPD Con- gress 1993, pp. 759-773.