The article presents the investigation results upon recovery of precious metals from electronics waste and used ceramic catalytic converters. Various frothing agents which generate stable and abundant foam as well as collectors and pH regulators have been used in the investigations. The tests were conducted with the use of laboratory flotation device

A. Blacha-Grzechnik

B. Oleksiak

G. Siwiec

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107METALURGIJA 52 (2013) 1, 107-110B. OLEKSIAK, G. SIWIEC, A. BLACHA-GRZECHNIKRECOVERY OF PRECIOUS METALS FROM WASTE MATERIALS BY THE METHOD OF FLOTATION PROCESSReceived – Prispjelo: 2012-06-04Accepted – Prihvaćeno: 2012-08-30Preliminary Note – Prethodno priopćenje ISSN 0543-5846METABK 52(1) 107-110 (2013)UDC – UDK 661.185:669.22=111B Oleksiak, G. Siwiec - Silesian University of Technology, Department of Metallurgy, Katowice, PolandA. Blacha-Grzechnik - Silesian University of Technology, Department of Chemistry, Gliwice, PolandThe article presents the investigation results upon recovery of precious metals from electronics waste and used ceramic catalytic converters. Various frothing agents which generate stable and abundant foam as well as collec-tors and pH regulators have been used in the investigations . The tests were conducted with the use of laboratory fl otation deviceKey words: fl otation, fl otation reagents, waste, silver, recycled.INTRODUCTIONFlotation is the method of separation commonly ap-plied to the enrichment process of carbon and metal ores. It is an effect related to various interfacial phe-nomena present in solid/liquid/gas system. If the grain shows the hydrophilic properties under certain deﬁ ned conditions then in the ﬂ otation process it can be separated from those that do not feature such properties [1-4]. The intensity of ﬂ otation process is determined by numerous factors the most important of which are: properties of ﬂ o-tation foam (type of frothing agent) and grain size. The ﬂ otation method can be used for separation of metal from grain fraction of some oxides and carbides. This was con-ﬁ rmed by test results obtained during recovery of native gold from polymetallic copper ores performed at CSIRO Minerals in Australia [5].The authors of the presented article conducted a number of tests on the recovery of silver from jewellery wastes and silver semi-products with the application of ﬂ otation process [6-7]. They made some attempts at the recovery of precious metals from waste printed circuits boards of mobile phones, PC computers and used ceramic catalytic convertors. The results obtained are presented in the article.In majority of PCBs cases, precious metals are coat-ed upon ceramic or plastic elements. The content of pre-cious metals in such products greatly depends on the age of the waste material. In the 80 s of the last century, the thickness of the layer upon contacts in electronic devices was 1-2,5 µm whereas now it is 300 – 600 nm. It is estimated that there is ca.1kg of silver and 0,3 kg of gold in only 1Mg of used mobile phones while 1 Mg of used computers contains 3 kg of silver and 0,3 kg of gold.End-of life catalytic reactors constitute another group of waste materials and have been used in vehicles since 2001. There are two types of catalytic convertors: ce-ramic and metal. In case of ceramic catalytic convertors the basic material is the mass which contains MgO, Al2O3 i SiO2 as well as ZrO and which is coated with precious metals from the platinum family: platinum, palladium, rhodium and occasionally ruthenium. The average platinum content in a catalyst is ca. 2 kg. The platinum content in a catalytic reactor is relatively high thus ca. 0,5 kg of platinum can be recovered from 1 Mg of reactors. In the view of the fact that this type of waste material is systematically growing, the process of its treatment seems to be vital.FLOTATION TEST STAND AND REAGENTS USED IN THE FLOTATION PROCESSFlotation test stand constructed as part of the pre-sented paper was designated for some laboratory at-tempts at selective separation of components in scrap materials. It consists of a ﬂ otation chamber made of Figure 1  The diagram of the device used in tests of fl otation process: 1 - the computer, 2 -the motor, 3 - the rotor, 4 – the fl otation cell, 5 - the drift fender, 6 - the fl otation concentrate cell108  METALURGIJA 52 (2013) 1, 107-110B. OLEKSIAK et al.: RECOVERY OF PRECIOUS METALS FROM WASTE MATERIALS BY THE METHOD…acid resistant steel and an engine-propelled rotor with height control device. The liquid is mixed by the rotor and air which is introduced by a compressor connected with the rotor. The rotor speed is set within the range from 100 – 1 500 rev/min whereas air ﬂ ow is controlled by a rotometer. The scum is collected from the chamber surface with a mechanical rake as the process continues. Figure 1 presents a diagram of the device used in tests of ﬂ otation process.Various types of frothing agents, collectors and pH regulators have been used for investigations. Table 1 presents the agents applied.Table 1 The agents appliedFoamingagentCollectingagentpHregulatorα-terpineol Acrylonitrile CuSO4corfl ot Sodium amyl xantho-genatePine oil Potassium etyl xantho-genateX-23PREPARATION OF THE MATERIAL FOR FLOTATION PROCESSIn the ﬁ rst stage of the carried out research, the printed circuit boards from PC computers and mobile phones have been subjected to crushing and grinding process.The following installation has been used in the investi-gations of the crushing process of waste materials which contain precious metals: screw mill, sharp mill, ball mill and buhr stone mill.In the course of the carried out investigations it was found that grinding of big size printed boards in a ball grinder does not bring satisfactory results. Although a sig-niﬁ cant part of the charge sustains ﬁ ne grinding, part of the post-process fraction retains the size which is not suitable for the process of ﬂ otation. This problem had been elimi-nated by the application of preliminary crushing with screw mill, before ball mill was used.Two-step grinding of printed circuit boards helps ob-tain the fraction with granularity proper for ﬂ otation proc-ess. Similarly satisfactory effect is obtained at additional grinding of the fraction initially reﬁ ned with screw mill and with the assistance of buhr stone mill or sharp mill.In all cases, classiﬁ cation of the materials obtained as the consequence of grinding was performed with LPzE-2e vibrating screen. Sieve analysis shows that in case of two-step crushing (screw mill - buhr stone mill, screw mill – sharp mill) the average 90 % of output fraction from mills shows the crushing which is appro-priate for ﬂ otation process. The remaining part (around 10 %) has to be subjected to additional grinding since it shows granularity above 0.2 mm. In case of the device system screw mill - ball mill, the proportions are slight-ly less favorable and their average value amounts from80 % to 20 %.Apparent improvement of grinding efﬁ ciency of such materials as printed circuit boards can be obtained by cooling them before they are introduced into crush-ing devices. An attempt was made with the application of liquid nitrogen. Crushing of ceramic catalytic con-vertors has to be a two stage procedure. The use of screw mill and then a ball mill, buhr stone mill or sharp mill assures positive effects. Sieve analysis shows that over 95 % of the output fractions (for three layouts of devices) presents granularity below 0.2 mm and thus is appropriate for ﬂ otation process.The material obtained after grinding process has been subjected to X-ray analysis and the analysis on atomic adsorption spectrometer. Three samples were taken from each type of waste material.Chemical analysis of used printed circuit boards per-formed upon atomic adsorption spectrometer is present-ed in Tables 2 and 3.Table 2  Chemical composition of printed circuit boards from PC computers / % wtSample number Ag Cu Pb1 0,044 23,6 4,762 0,0017 26,8 5,243 0,011 27,8 6,01Table 3  Chemical composition of printed circuit boards from mobile phones / % wtSample number Ag Cu Pb1 0,044 23,6 4,762 0,0017 26,8 5,243 0,011 27,8 6,01Chemical analysis performed upon atomic adsorp-tion spectrometer proved that the platinum content in crushed fraction of ceramic catalytic convertors is 0,026 %.THE INVESTIGATIONS RESULTS OF FLOTATION PROCESSIn order to learn more about ﬂ otation kinetics in combinations ceramics-metallic fraction, polymer-me-tallic fraction, ceramics-polymer-metallic fraction which are quite essential when wastes containing pre-cious metals are dealt with, the authors performed a se-ries of tests with the use of synthetic mixtures. Silver powder and ceramic materials from the wastes contain-ing precious metals i.e. aluminum oxide, silicon oxide and epoxy resin (typical representative of polymers) have also been used for tests.The carried out research were to determine the con-ditions of ﬂ otation process of materials included in waste materials which occur in a real world. The ob-tained results were satisfactory therefore further tests were performed on real materials. Tables 4 and 6 present exemplary test results of ﬂ otation process performed upon crushed printed circuits from PC boards.109METALURGIJA 52 (2013) 1, 107-110B. OLEKSIAK et al.: RECOVERY OF PRECIOUS METALS FROM WASTE MATERIALS BY THE METHOD…Tables 7-8 depict exemplary tests results of ﬂ otation process performed upon crushed printed circuits from mobile phones.Table 6  Results of the fl otation tests for printed circuit boards from PC computers using Corfl ot as frothing agent and X-23 as collectorRotation frequency equal /rot/minpHContent in fl otate/ % wt.Ag content in chamber residues /% wt.Ag Cu PbAir fl ow rate 2 /dm3/min5006 0,012 10,60 1,65 0,117 0,011 8,34 1,45 0,168 0,007 6,28 1,22 0,2610 0,003 6,12 1,05 0,45Air fl ow rate 4 /dm3/min7006 0,014 10,16 1,64 0,097 0,009 8,12 1,32 0,108 0,001 6,13 1,13 1,1710 0,000 6,04 1,00 0,33Table 4  Results of the fl otation tests for printed circuit boards from PC computers using pine oil as frothing agent and oleic acid as collectorRotation frequency equal /rot/minpHContent in fl otate/ % wt.Ag content in chamber residues /% wt.Ag Cu PbAir fl ow rate 2 /dm3/min5006 0,055 8,6 4,2 0,0017 0,032 5,6 1,2 0,0048 0,029 8,8 2,2 0,00310 0,020 6,3 1,6 0,004Air fl ow rate 4 /dm3/min7006 0,074 9,7 1,6 0,0027 0,060 9,8 1,1 0,0038 0,026 8,0 2,1 0,00210 0,018 7,7 1,8 0,004Table 5  Results of the fl otation tests for printed circuit boards from PC computers using Corfl ot as frothing agent and X-23 as collectorRotation frequency equal /rot/minpHContent in fl otate/ % wt.Ag content in chamber residues /% wt.Ag Cu PbAir fl ow rate 2 /dm3/min5006 0,099 6,0 0,92 0,0017 0,097 6,0 0,91 0,0018 0,090 6,3 0,99 0,00210 0,072 7,8 1,01 0,003Air fl ow rate 4 /dm3/min7006 0,096 7,8 0,93 0,0017 0,061 6,8 0,97 0,0058 0,059 5,7 1,04 0,00610 0,023 5,2 1,82 0,007Table 8  Results of the fl otation tests for printed circuit boards from mobile phone using Corfl ot as frothing agent and sodium etyl xanthogenate as collectorRotation frequency equal /rot/minpHContent in fl otate/ % wt.Ag content in chamber residues /% wt.Ag Au CuAir fl ow rate 2 /dm3/min5006 0,2 0,05 15,7 0,137 0,2 0,06 14,1 0,288 0,4 0,04 11,1 0,2710 0,2 0,05 16,3 0,23Air fl ow rate 4 /dm3/min7006 0,2 0,03 16,9 0,147 0,2 0,04 16,0 0,198 0,1 0,04 14,0 0,1810 0,1 0,03 13,5 0,14Table 7  Results of the fl otation tests for printed circuit boards from mobile phone using Corfl ot as frothing agent and sodium amyl xanthogenate as collectorRotation frequency equal /rot/minpHContent in fl otate/ % wt.Ag content in chamber residues /% wt.Ag Au CuAir fl ow rate 2 /dm3/min5006 0,16 0,04 17,2 0,127 0,11 0,02 10,1 0,248 0,13 0,06 12,1 0,1710 0,15 0,05 17,9 0,13Air fl ow rate 4 /dm3/min7006 0,17 0,03 16,9 0,137 0,15 0,02 16,0 0,208 0,13 0,05 14,1 0,1710 0,14 0,04 13,6 0,14The application of different ﬂ otation parameters i.e. the change of gas ﬂ ow, rotor speed and ﬂ otation rea-gents did not affect the scum enrichment.The tests results of ﬂ otation process carried out upon ground ceramic catalytic convertors are presented in Ta-ble 9.The application of different ﬂ otation parameters i.e. gas ﬂ ow above 2 dm3, rotor speed 700 and different rea-gents than those presented in Table 9 did not bring sat-isfactory ﬂ otation results ( slight platinum enrichment in the scum as compared with the initial content).110  METALURGIJA 52 (2013) 1, 107-110B. OLEKSIAK et al.: RECOVERY OF PRECIOUS METALS FROM WASTE MATERIALS BY THE METHOD…CONCLUSIONSThe parameters of ﬂ otation process and ﬂ otation re agents applied and presented in the paper, in case of waste printed circuit boards from mobile phones and PC boards, did not bring satisfactory results (though the results obtained with synthetic materials were promis-ing). The obtained scum did not exhibit high content of precious metals. However, the increase of silver con-centration in the ﬂ otation chamber (Table 6) was ob-served.Promising results, on the other hand, were obtained from the tests on end-of-life ceramic catalytic conver-tors used in vehicles. The best results were obtained for rotor speed of 500 rev/min and gas ﬂ ow of 2 dm3/min. In case of these wastes the best results were obtained for the following reagents:Frothing agents: corﬂ ot,• Collecting: sodium amyl xanthogenate, X-23, ethyl • xanthogenate.The application of such reagents helped obtain plati-num concentration in a ﬁ nal product up to 0,38 % which is close to its concentration in anode slime obtained in the process of copper electroreﬁ ning. The application of slightly different ﬂ otation conditions (the same as in case of wastes from ﬁ nal treatment of silver semi-prod-ucts and jewellery) i.e. gas ﬂ ow above 2 dm3 rotor speed 700 and different foaming reagents, did not bring satis-factory ﬂ otation results (slight platinum enrichment in the scum as compared with its initial content).REFERENCES[1]  Drzymała J.: Podstawy mineralurgii, Wyd. Pol. Wroc., Wrocław (2001).[2]  Burdzik R., Folęga P., Węgrzyn T. Silva Abílio P.: Con-ferencia Engenharia’2009, Covilha Portugalia, 2009, p. 168-171.[3]  Pałucha K.: Prace i Materiały Wydziału Zarządzania Uni-wersytetu Gdańskiego Sopot (2011) 4/6, 317-327.[4]  Kolmasiak C.: Hutnik -Wiadomości Hutnicze (2010) 5, 252-255.[5]  Iskra J.: Ceramics International 23 (1997), 337 - 342.[6]  Oleksiak B., Blacha-Grzechnik A., Siwiec G; Metalurgija 51 (2012) 1, 97-100.[7]  Oleksiak B, Blacha-Grzechnik A., Siwiec G; Metalurgija 51 (2012) 3, 298-300.Note: Nowak P is responsible for English language, Katowice, PolandTable 9  The results of the fl otation tests carried out upon ground ceramic catalysts with the use of Corfl ot as a frothing agent, selected collecting reagents and CuSO4 as pH regulator (gas fl ow rate 2 dm3/min, rotation speed – 500 rot/min.)Collector reagent pHContent in fl otate/ % wt.Pt content in chamber residues/ % wt.---------- 7,01 0,19 0,012Ksantog amylowy 10,03 0,32 0,001 Ksantog amylowy 8,00 0,34 0,001 Ksantog etylowy 10,01 0,14 0,018Ksantog -etylowy 8,00 0,38 0,001 X-23 10,03 0,33 0,001 X-23 8,03 0,30 0,003 Akrylonitryl 10,01 0,12 0,015Akrylonitryl 8,04 0,32 0,001 

Recovery of precious metals from waste materials by the method of flotation process

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