Scientific Journal of Riga Technical University Material Science and Applied Chemistry
2011
_________________________________________________________________________________________________ Volume 23
Electrodialysis System for Electrodeposition of Gold from Non-cyanide Solutions Tatiana Sadyrbaeva, Institute of Inorganic Chemistry of the Riga Technical University Abstract. The process removal of gold(III) ions from hydrochloric solutions containing 0.01 mol/l HAuCl4 accompanied with metal electrodeposition from cathodic noncyanide solutions is studied at galvanostatic electrodialysis. A possibility of gold(III) electrodeposition from 0.1 mol/l solutions of sulphuric, nitric, hydrochloric, perchloric acids and ammonia is demonstrated. The gold electrodeposits with good adhesion and of bright appearance are obtained in all studied systems. The effects of the main electrodialysis parameters as well as of the composition of the cathodic solution on the gold(III) transport and electrodeposition rate are determined. Keywords: gold, electrodialysis, electrodeposition, non-cyanide electrolytes, coatings
I. INTRODUCTION Gold coatings are currently widely used for their decorative, technical and functional properties in jewellery, in manufacturing of electronics, in aerospace and automotive industries, telecommunications, medicine and dentistry [1-4]. The most important industrial use of gold is in electronic devices. The use of gold in the electronics industry arises primarily because of its excellent corrosion resistance, solderability and bondability and its high electrical and thermal conductivity. Gold is used in connectors, switch and relay contacts, soldered joints, connecting wires and connection strips [3]. Traditionally, gold has been plated from gold cyanide electrolytes [3,5,6]. The main disadvantage of cyanide baths is their high toxicity. The other problem of using cyanide electrolytes is that they are often incompatible with micro device manufacture. Interest in developing nontoxic gold electrolytes has grown rapidly in recent years [7,8]. The most common non-cyanide gold electrolyte is based on a gold-sulphite complex. Gold sulphite baths are non-toxic and are widely used for microelectronic and optoelectronic applications. However, they are unstable under neutral or slightly acidic conditions necessary for optimum resist compatibility [8]. A gold-thiosulphate complex has not been used successfully for making a practical bath due to the instability of thiosulphate ion itself with respect to its disproportionation reaction [7]. Sulphur precipitation occurs in thiosulphate electrolyte and disproportionation of gold occurs in sulphite electrolyte. The mixed ligand system containing both thiosulphate and sulphite has been proposed in [9, 10]. It was found that mixed bath had higher stability than either the pure thiosulphate or sulphite baths and can operate stably at near neutral pH. However, the adhesion of deposits obtained from the mixed bath is worse if compared with the pure sulphite bath [8]. The alternative non-cyanide gold plating electrolytes have been proposed, such as nitro-sulphito [11],
mercapto-alkylsulphonic and hydantoin baths [8]. Unfortunately, new non-toxic gold electrolytes are not widely used in industry. The non-cyanide baths usually show instability, which manifests itself in the formation of colloidal gold. Electroplating baths formulated from Au(III) complexes are relatively rare [8]. It should be noted that hard gold, which is used widely in connectors or jewellery, presently can be plated only from cyanide-based baths [7]. Therefore, the development of new gold plating baths, which are environmentally friendly and produce high quality gold deposits, is of great practical value. The process of silver(I) electrodeposition during extraction from nitric acid solutions through the bulk liquid membranes containing a cation-exchange carrier was studied by the author previously [12]. It was found that silver deposits obtained from diluted perchloric acid solutions were dense, smooth, with good adhesion. Gold(III) exists mainly as anionic chlorocomplex [AuCl4]− in hydrochloric solutions [1], therefore, metal transport into the cathodic solution can occur only by diffusion. In this paper, the gold(III) ions transfer process across inert semipermeable films is studied at galvanostatic electrodialysis and optimal conditions for gold electrodeposition from non-cyanide cathodic solutions are determined. II. MATERIALS AND METHODS A. Instrumentation The experiments were carried out in a three-compartment Teflon electrodialysis cell in the system: (+) Pt H2SO4 HAuCl4 cathodic solution Pt (−) HCl The cathodic solution (volume 17 cm3) was separated from the feed solution (volume 13 cm3) by the cellophane film. The anodic solution (volume 17 cm3) containing 0.15 mol/l H2SO4 was separated by the solid cation exchange membrane MK-40 from the feed solution. The solutions were not agitated. The cellophane films and the solid membranes were soaked in water for more than 24 h before use. The direct electric current was supplied to the plane platinum electrodes (surface area 7.1 cm2). Potentiostat P-5848 (Russia) was used as a current source. Voltage was measured by digital voltmeter. The concentration of gold(III) in the solutions was determined by spectrophotometry by characteristic absorption peak at 311 nm [13]. UV-Vis spectrophotometer СФ-46 (Russia) was used for the analysis of gold(III) ions. The measurements were carried out at room temperature.
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Scientific Journal of Riga Technical University Material Science and Applied Chemistry
2011
_________________________________________________________________________________________________ Volume 23 B. Reagents and materials 10 8 Voltage (V)
The feed solution was prepared by dissolving metallic gold in aqua regia. It contained as a rule 0.01 mol/l HAuCl4 in 1.0 mol/l HCl. Reagents of pro-analysis grade were used without further purification. The solid cation exchange membrane MK-40 was a sulfonic polystyrene divinylbenzene membrane. The cellophane films had a thickness of 20-30 μm and a surface area of pores of 1∙10−3 cm2 / 1 cm2.
6 4
III. RESULTS AND DISCUSSION It has been found that without electric field application about 23% of gold(III) is transferred across the cellophane membrane from the feed hydrochloric solution into the solution of 0.1 mol/l H2SO4 within 1 hour. The electrodeposition of gold on the platinum cathode is observed during electrodialysis. Gold(III) anions are transported into the cathodic solution only by diffusion. The polarity of the electric field prevents gold electromigration in this direction. AuCl4− ions are not transferred into the anodic solution as the anodic compartment is separated by the solid cation exchange membrane. It was found that the electrodeposition of gold proceeded with an approximately equal rate from diluted solutions of sulphuric, nitric, hydrochloric, perchloric acids and ammonia (Table 1). The [AuCl]4− transport rate from the feed solution also poorly depends on the cathodic solution composition, since it is determined, obviously, by the gold(III) ions diffusion across the cellophane film. The bright, smooth and dense gold deposits with good adhesion to the cathode were obtained in all studied systems. To study the main regularities of the electrodialysis, sulphuric cathodic solution was selected because the highest electrodeposition degree was achieved in this system. The voltage in the membrane systems containing solutions of acids is 3 − 4 V at the current density 5.6 mA/cm2 and poorly changes during electrodialysis, whereas the initial voltage in a system with ammonia solution is significantly higher (Fig. 1). TABLE 1
2 0 0
10
20
30 40 Time (min)
50
60
Fig. 1. Change in voltage during electrodialysis for various cathodic solutions (i = 5.6 mA/cm2; cathodic solution (0.1 mol/l): ● - NH4OH; ▲– HCl; 3 ○– HNO3).
The electrical conductivity of the weak electrolyte – NH4OH solution is lower in comparison with strong acids solutions. During the electrodialysis hydrogen ions and [AuCl]4− anions are transferred into the cathodic solution, the electrical conductivity of the system rises and voltage decreases. Fig. 2 presents the influence of the current density on the rates of gold(III) transport and electrodeposition. The gold(III) transport rate from the feed solution is practically independent of the current density, as the transport of [AuCl] 4− into the cathodic solution takes place due to diffusion. The electrodeposition rate increases and the metal content in the cathodic solution decreases when the current density comes up to 6 mA/cm2. At higher current densities the electrodeposition degree does not change. The current efficiency of the deposition process is less than 10 % for the studied system and is found to decrease with the current density rise. The increase of the current efficiency can be achieved using more concentrated gold(III) solutions and by raising temperature.
EFFECT OF CATHODIC SOLUTION COMPOSITION UPON THE GOLD(III) TRANSPORT AND ELECTRODEPOSITION
30
(CAu = 0.01 mol/l; i = 5.6 mA/cm2; t = 60 min) Gold content (%) Feed solution
Cathodic solution
25 Cathode
H2SO4
74.6
7.2
14.3
HClO4
77.3
6.4
14.1
NH4OH
72.5
8.5
13.4
HCl
76.1
7.3
12.6
HNO3
74.7
8.8
10.4
Removal degree, Gold content (%)
Cathodic solution (C = 0.1 mol/l)
20 15 10 5 0 0
3 6 9 12 Current density (mA/cm2)
15
Fig. 2. Effect of current density on gold(III) removal degree from the feed solution (●), metal content on the cathode (▲) and gold(III) content in the cathodic solution (○) (t = 60 min; cathodic solution – 0.1 mol/l H2SO4).
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Scientific Journal of Riga Technical University Material Science and Applied Chemistry
2011
_________________________________________________________________________________________________ Volume 23 100
12 10
Voltage (V)
Gold content (%)
80 60 40 20
8 6 4 2
0
0 0
0.5
1
1.5 Time (h)
2
2.5
3
0
10
20
30 40 Time (min)
50
60
Fig. 3. Kinetics of gold(III) removal from the feed solution (●), electrodeposition degree (▲) and metal accumulation in the cathodic solution (○) (i = 8.5 mA/cm2 ; cathodic solution – 0.1 mol/l H2SO4).
Fig. 4. Change in voltage during electrodialysis for various H2SO4 concentrations in the cathodic solution (i = 8.5 mA/cm2; СH2SO4 (mo/l): ● – 0; ▲ – 1∙10-4; □ – 1∙10-3; ○ – 0.1).
More than 45 % of gold(III) is transported from the feed solution containing 0.01 mol/l HAuCl4 into the cathodic solution and about 35 % of metal is electrodeposited on the cathode within 3 h of electrodialysis at the current density 8.5 mA/cm2 (Fig. 3). The mass of cathodic deposit continuously increases during electrodialysis, whereas the gold(III) concentration in the cathodic solution has its maximum value at 30 min. The gold(III) content in the cathodic compartment is less than 3 % after 3 hours of electrolysis. The current efficiency has its maximum value within 1 − 1.5 h, but does not exceed several per cent at the experimental conditions. The influence of the sulphuric acid concentration in the cathodic solution on the gold(III) electrodeposition rate was studied using 10─4 – 1 mol/l H2SO4 solutions. Results are given in Table 2. Change in H2SO4 concentration poorly effects the [AuCl]4− transport rate into the cathodic solution and electrodeposition rate. The transfer and electrodeposition of gold proceed with approximately the same rate even when distilled water is used as a cathodic solution. However, H2SO4 concentration significantly influences the shape of the voltage–time diagrams (Fig. 4). A sharp decrease of voltage
occurs in the beginning of electrodialysis in case of low (СH2SO4 ≤ 10-3 mol/l) acid concentration in the cathodic solution. In these systems a rather low initial electrical conductivity increases during electrodialysis due to the transport of hydrogen ions and gold(III) anions across the cellophane film into the cathodic solution. IV. CONCLUSIONS The electrodialysis technique with an inert and a cation exchange membranes allows to obtain gold electrodeposits with high quality and good adhesion to the cathode from diluted solutions of sulphuric, nitric, hydrochloric, perchloric acids, ammonia and water during removal from hydrochloric solutions. The gold(III) electrodeposition degree increases as the current density (0 – 6 mA/cm2) and the process duration (0 – 3 h) increase. Composition and concentration of acid in the cathodic solution poorly effect the gold(III) transport and electrodeposition rate as well as characteristics of the deposits. REFERENCES 1.
TABLE 2
2.
EFFECT OF H2SO4 CONCENTRATION IN THE CATHODIC SOLUTION UPON THE 2 GOLD(III) TRANSPORT AND ELECTRODEPOSITION (i = 8.5 mA/cm ; t = 60 min)
3.
Gold content (%)
СH2SO4 (mol/l)
Feed solution
Cathodic solution
Cathode
0
72.8
8.5
12.8
1∙10-4
72.3
8.0
13.8
1∙10
-3
78.1
6.9
12.8
1∙10-2
74.1
5.4
14.5
0.1
74.4
7.1
14.9
1.0
−
−
13.4
4. 5. 6.
7.
8.
Бусев, А.P., Иванов, В.М. Аналитическая химия золота. Москва: Наука, 1973. 264 стр. Rapson, W.S., Groenewald, T. Gold Usage. London: Academic Press Inc, 1978. 352 pp. Christie, I.R., Cameron, B.P. Gold Electrodeposition within the Electronics Industry. Gold Bulletin, 1994, vol. 27, N 1, p. 12-20. Zielonka, A.R. Present Status and Future Developments in the Electroplating of Gold. Gold Bulletin, 1996, vol. 29, N 1, p. 17-18. Reid, F.H., Goldie, W. (Eds.) Gold Plating Technology . Ayr, Scotland : Electrochemical Publications Ltd., 1974. 352 pp. Kohl, Paul A. Electrodeposition of Gold. In: Schlesinger, M., Paunovic M. (Eds.) Modern Electroplating. John Wiley and Sons, New York, 2000, p. 201-226. Kato, C.M., Okinaka, Y. Some Recent Developments in Non-Cyanide Gold Plating for Electronics Applications. Gold Bulletin, 2004, vol. 37, N 1-2, p. 37-44. Green, T.A. Gold Electrodeposition for Microelectronic, Optoelectronic and Microsystem Applications. Gold Bulletin, 2007, vol. 40, N 2, p. 105-114.
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Scientific Journal of Riga Technical University Material Science and Applied Chemistry
2011
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Osaka, T., Kodera, A., Misato, T., et. al. Electrodeposition of Soft Gold from a Thiosulfate-Sulfite Bath for Electronics Applications. Journal of Electrochemical Society, 1997, vol. 144, N 10, p. 3462-3469. 10. Liew, M.J., Sobri, S., Roy, S. Characterisation of a thiosulphatesulphite gold electrodeposition process. Electrochimica Acta, 2005, vol. 51, N 5, p. 877-881. 11. Hydes, P., Middleton, H. The Sulphito Complexes of Gold, their chemistry and applications in gold electrodeposition. Gold Bulletin, 1979, vol. 12, N 3, p. 90-95. 12. Садырбаева, T.Ж. Мембранная экстракция и электроосаждение серебра(I) в системах с ди(2-этилгексил)фосфорной кислотой. Журнал прикладной химии, 2007, т. 80, № 11, стp. 1839-1844.
13. Марченко З. Фотометрическое определение элементов. Москва: Мир, 1971. 504 стр. Sadyrbaeva T. graduated from the Faculty of Chemistry of Latvian State University,. She obtained Dr. Chem in 1993 at the Institute of Inorganic Chemistry of the Latvian Academy of Sciences. The author’s major field of study is Electrochemistry. Researcher at the Laboratory of Electrochemistry of the Institute of Inorganic Chemistry of Riga Technical University for the past seventeen years. Research interests include electrodialysis through liquid membranes, electrodeposition, separation of metals, liquid extraction. E-mail:
[email protected].
Tatjana Sadirbajeva. Elektrodialīzes sistēma zelta elektroizgulsnēšanai bezcianīdu šķīdumos Ar mērķi izstrādāt jaunu ekoloģiski tīru un resursus taupošu tehnoloģiju zelta elektroizgulsnēšanai no netoksiskiem šķīdumiem, kuri varētu aizvietot cianīdu elektrolītus, pētīts zelta(III) jonu elektroizgulsnēšanas process izdalot to no atšķaidītiem sālsskābes šķīdumiem galvanostatiskās elektrodialīzes apstākļos. Pētījumos tika izmantota trīskameru elektrodialīzes šūna, kurā anoda šķīdums atdalīts no izejas zelta(III) šķīduma ar katjonu apmaiņas membrānu un katoda šķīdums atdalīts ar inertu celofāna membrānu. Noteikts, ka uzliekot elektrisko lauku notiek [AuCl]4− anjonu difūzijas pārnese caur inerto membrānu katodšķīdumā un zelta elektroizgulsnēšana uz katoda. Parādīta iespējamība zelta elektroizgulsnēšanai no atšķaidītiem sērskābiem, slāpekļskābiem, sālsskābiem, perhlorskābiem un amonjaka šķīdumiem. Konstatēts, ka izturīgas, sīkkristāliskas zelta nogulsnes, kas labi turās uz katoda, izdalās visās izpētītajās sistēmās. Noteikts, ka palielinot strāvas blīvumu intervālā 0 – 6 mA/cm2 un procesa ilgumu, pieaug zelta elektroizgulsnēšanas pakāpe. Parādīts, ka zelta izdalīšanas pakāpe no izejas šķīduma, kas satur 0,01 M HAuCl4 1 M sālsskābē, sasniedz 45 % un 35% metāla izgulsnējās uz katoda pēc 3 stundām elektrodialīzē ar strāvas blīvumu 8,5 mA/cm2. Noteikts, ka sērskābes koncentrācijas izmaiņa katodšķīdumā no 0 līdz 1 M un katodšķīduma sastāvs maz ietekmē zelta jonu pārneses un elektroizgulsnēšanas ātrumu. Татяна Садырбаева. Электродиализная система для электроосаждения золота из бесцианидных растворов С целью изучения возможности получения золотых покрытий из нетоксичных растворов, способных заменить применяющиеся в настоящее время цианидные электролиты золочения, исследован процесс электроосаждения ионов золота(III) при извлечении из разбавленных солянокислых растворов в процессе гальваностатического электродиализа. В экспериментах использовали трехкамерный электродиализатор, в котором анодный раствор был отделен от исходного раствора золота(III) катионообменной мембраной, а катодный раствор ─ инертной целлофановой мембраной. Показано, что при наложении электрического поля происходит диффузионный перенос анионов [AuCl] 4− через инертную мембрану в катодный раствор и электроосаждение золота на катоде. Установлено, что данный метод позволяет осуществить катодное электроосаждение золота из разбавленных растворов серной, азотной, соляной, хлорной кислот, аммиака и воды. Показано, что во всех изученных системах выделяются блестящие, мелкокристаллические, прочно сцепленные с катодом осадки золота. Установлено, что эффективность электроосаждения катионов Ag+ возрастает при повышении плотности тока электродиализа в интервале 0 – 6 мА/см2 и продолжительности процесса (0 – 3 час). Показано, что степень извлечения золота(III) из исходного раствора, содержащего 0,01 М HAuCl4 в 1,0 М HCl, составляет 45%, при этом 35% металла осаждается на катоде после 3 часов электродиализа с плотностью тока 8,5 мА/см2. Установлено, что изменение концентрации серной кислоты в катодном растворе (0 – 1,0 М), а также состав катодного раствора слабо влияют на степень извлечения и электроосаждения золота(III).
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