Photo induced dissociation of ferri and ferro cyanide in hydroponic solutions

Abstract

ABSTRACT:The potential for photo-induced dissociation of ferri-and ferro-cyanide was investigated. The overall reactions followed first order kinetics, judged by the free cyanide analyzed in aqueous solution. The dissociation rates for ferri-and ferro-cyanide were mathematically described by the equations:respectively. In addition, photo-induced dissociation of both iron cyanides was enhanced under an alkaline environment than a neutral condition. Results from the temperature-dependent tests indicated that the dissociation rate of ferricyanide was significantly higher than that of ferro-cyanide at all treatment temperatures. The kinetic parameter, activation energy (E a ) was also experimentally determined to be 12.02 and 12.32 kJ/mol for ferri-and ferro-cyanide, respectively. The results obtained suggest that both iron cyanides are susceptible to photo-dissociation and the rates are positively correlated to the change of temperatures. The information collectively also has important implications for waste management of iron cyanides as well as for risk assessment in a field trial.

Uptake, assimilation and toxicity of cyanogenic compounds in plants: facts and fiction

“…Indeed, decomposition of iron cyanides into free cyanide in soils in the absence of light was detected at pH of 3.8 and 4.2, and the rate appears to be inversely related to pH of ambient environment, while the half-life of iron cyanides was estimated to be approximately 100 years at pH of 6.5 using a decomposition model (Meeussen et al 1992). It is also experimentally confirmed that dissociation rate of ferri-cyanide is significantly higher than that of ferro-cyanide in the presence of light (Yu et al 2011b). Additionally, graminaceous plants have evolved a specific mechanism to acquire Fe through a chelation-based strategy (Kim and Guerino 2007).…”

“…and free cyanide (CN -) as a complex without liberation. Obviously, changes in physicochemical conditions in the environment will affect and/or alter speciation of iron cyanides (Zagury et al 2004;Yu et al 2011bYu et al , 2012b. Indeed, decomposition of iron cyanides into free cyanide in soils in the absence of light was detected at pH of 3.8 and 4.2, and the rate appears to be inversely related to pH of ambient environment, while the half-life of iron cyanides was estimated to be approximately 100 years at pH of 6.5 using a decomposition model (Meeussen et al 1992).…”

“…It is known that the equilibrium constants (logK) are 45.61 and 52.63 for ferro-and ferri-cyanide, respectively (Meeussen et al 1992), while the logK value of Fe-phytosiderophores is only 18.1 (Mino et al 1983). Therefore, liberation of both chemicals is highly unlikely to occur in the solution, due to the presence (Yu et al 2011b(Yu et al , 2012b reductase at root cell's plasma membrane (Kim and Guerino 2007). However, there is no literature available to proof this Fe-acquisition process during phyto-assimilation of iron cyanides.…”

“…After entering the plant materials, distribution of cyanide in different parts of plant materials was largely dependent on the chemical species of cyanide present during phyto-transport. It is known that the fate of different species of cyanide in plants was quite different (Larsen et al 2005;Larsen and Trapp 2006;Yu and Gu 2010;Yu et al 2011b. Indeed, free cyanide is able to enzymatically degrade through the defined degradation pathways (described in ''Assimilation of free cyanide'' section), where phyto-degradation of iron cyanides is apparent, but the degradation pathway is still under investigation (discusses in ''Biotransformation of iron cyanides'' section).…”

“…It has been observed that free cyanide did not accumulate in healthy plants (Larsen et al 2005). When plants were exposed to iron cyanides, amounts of cyanide detected as total cyanide were significantly higher than the background, implying that both iron cyanides were probably still in the same original complexed form in plant materials (Larsen and Trapp 2006;Yu and Gu 2010;Yu et al 2011b. Additionally, the enzyme b-cyanoalanine synthase responsible for phyto-assimilation of free cyanide has been widely observed in different plants.…”