ABSTRACT
Certain thermal technologies can be used to destroy all forms of cyanide, including the strong metal-cyanide complexes (e.g., iron and cobalt) in both solid and liquid wastes. Generally these technologies involve both high temperature and pressure, and they tend to be relatively expensive to implement and operate when compared to ambient-temperature treatment options (e.g., adsorption, ion exchange, and chemical precipitation processes — see Chapters 20, 21, and 23). However, given the right set of circumstances, these thermal technologies can be cost effective, for example, when dealing with small quantities of waste and off-site thermal treatment facilities are available. The following thermal technologies are described in detail in the following sections:
• High temperature alkaline hydrolysis • High temperature alkaline chlorination • Incineration or thermal treatment • Electrolytic oxidation or (decomposition) • Calcium polysulfide treatment • Wet air oxidation
These technologies have been applied for the treatment of water, soil slurries, and sludges containing free cyanide, weak metal-cyanide complexes, and strong metal-cyanide complexes. Descriptions for the technologies follow, and include the following main features:
• Process description and implementation • Achievable treatment levels • Design considerations • Critical design conditions • Residuals generated • Technology complexity
• Cost information • Status of technology implementation
The chapter concludes with a technology summary matrix (Table 22.3) for the thermal technologies discussed here. Only some of the technologies have been demonstrated at full-scale.
