Formation and Evaluation of Cyanide from Cyanide Free Solution By Electroplating

Abstract

In recent years, environmental problems are regarded as important in all industries. Especially in the plating industry, cyanide, which is a toxic substance is strictly regulated, plating bath with cyanide and plating bath without cyanide are strictly distinguished. This is carried out on the premise that cyanide is not generated from a plating bath without cyanide. As such cyanide compounds are severely regulated, there are adverse effects such as cyanide spill accidents, waste water treatment must be done, so stop using cyanide compounds and use raw materials and manufacturing methods not containing cyanide compounds it tends to be. However, when defected samples plated from bath without cyanide was analyzed by using thermal desorption spectrometry (TDS), The bath with synthesized cyanide was removed by activated carbon treatment, but it was confirmed that cyanide was formed even in a plating bath without cyanide. The case where cyanide was detected from a cyanide-free plating bath was also reported in the 1980's,1) it had reported that it was possible to synthesize cyanide when carbon source and nitrogen source were present and conditions were set there.2) It was also reported amines and nitrite ion reacted and formed cyanide.3) We have reported that the cyanide was synthesized in the solution containing glycine.4) All plating baths were adjusted to 0.2 mol/dm3. Bath pH was adjusted at 12.0. Plating conditions were as follows, anode was nickel, cathode was platinum, a current density was controlled from 10 A/dm2 bath temperature was 60 °C. A electrolysis time was controlled from 60 min. Cyanide concentration was determined by the pack test and the picric acid method. The pack test is used to determine the presence or absence of cyanide. The picric acid method was used to determine cyanide concentration in the bath. Figure 1 showed effect of chemicals, amine and amino acid, on amount of synthesized cyanide. However, the amount of cyanide produced by amines was as low as 0.1 ppm for N-methylethylene-diamine (N-MEDA) and 4.7 ppm for N-ethyl ethylene-diamine (N-EEDA). Among the amino acids, without glycine the maximum of β-alanine was about 6.6 ppm, and the minimum was less than 0.1ppm. However, when a glycine bath was used, cyanide of 50.9 ppm could be measured. Glycine bath was found to be easy to produce cyanide.1) M.Nonomura, Jitsumu Hyomen Gijyutsu, 32(1), pp11-20 (1985) [in Japanese]2) M.Hara and T.Ishikawa, Mizusyorigijyutsu, 22(3), pp215-218 (1981) [in Japanese]3) T.Koshimizu, K.Takamatsu, M.Kaneko, S.Fukui and S.Kanno, HyGienic Chemistry, 21(6), pp326-329 (1975) [in Japanese]4) S.Mizuhashi, T.Arakawa, N.Watanabe, S.Koike, M.Urano, K.Maejima, N.Hirashita and I.Koiwa, Electrochemistry, 84(6), pp394-397 (2016) [in Japanese] Figure 1