AAQTIC investigate cyanide in tannery effluent
12 August 2011AAQTIC, the Argentine Leather Chemists and Technicians Association, published a new report in July on cyanide levels in tannery effluent. The full report is available in both English and Spanish on their website.
The findings made on the cyanide issue that worried the tanning industry in Argentina throughout 2010. The detection of cyanide in effluents was taken from several tanneries for the AAQTIC report.
Cyanide concentration values in tanning effluents were measured and they turned out to be higher than the permitted 1 mg/l (1ppm) according to the Standard Method (20th Edition) for total cyanide or 0.1mg/l of cyanide detectable by chlorination according to the Standard Method CN 4500 (paragraphs C and E). As a result, penalties such as plant closures were applied to the tanners.
This situation has no precedents in the national and international tanning industry and, to confirm the results, some local authorities in Argentina employed consultants including foreign consultants to confirm the findings.
In view of the results and knowing that tanners do not use cyanide in products for their processes, it was decided that different alternative sources be researched.
It has been established that it is a complex issue. Conclusions are incomplete and further studies have to be carried out.
The purposes of the current investigations were:
- To understand the definition of cyanide pursuant to standards.
- To know how to prepare and preserve the samples to be analysed.
- To understand the different laboratory methods to measure cyanide levels and challenge the values obtained and potential interferences that may appear.
- To analyse which chemical products may generate cyanide under certain special pH and temperature conditions, and presence of oxidants, among others.
The research highlighted several issues since the different detection methods produced different cyanide values for the same effluent sample.
The most controversial chemical product ,which should be studied further is the use of TCMTB based fungicides (C9H6N2S3) which is the 2-(thiocyanomethyl) benzothiazole.
AAQTIC report that TCMTB manufacturer, Buckman, have said that the TCMTB molecule does not generate detectable levels of cyanide under regular conditions of application and treatment of tanning effluents, if the analytical methods are appropriate. The TCMTB chemical formula does not contain a labile cyanide group under normal industrial conditions.
Despite the remarks based on the need to treat TCMTB as interference in the analyses, many tanneries in Argentina had to stop using TCMTB in their processes say the authors of the report.
Another important issue is that future analysis should be performed jointly with the Government bodies in Argentina to know the correct detection methods to be used, and to make sure that they are applied by qualified people, in contact with the respective tannery technical departments.
According to the information gathered in the inspected companies, the method used by the governmental controlling authority is not the one stated by law in Argentina, and the tests performed show that different methods lead to different results.
Sodium hypochlorite oxidation is the customary method for the elimination of cyanide from industrial effluents where cyanide salts are used (eg electroplating). It has been confirmed that in the case of an effluent treated following the retanning process with limit values of 700 mg/l of COD and 200mg/l of BOD the addition of sodium hypochlorite has caused an increase in the concentration of cyanide by chlorination detected by the laboratory method.
For a complete version of the report in Spanish, visit:
http://www.aaqtic.org.ar/jornadaIII/pdf/cianurov12.pdf
In English, visit:
