Abstract
A real electroplating wastewater, containing 51,190 mg/L of free cyanide (CNf), 4899 mg/L of Ni and 1904 mg/L of Cu, was treated with calcium alginate hydrogel beads (CAB), pure or impregnated with biodegraded grape marc (EBGM) or activated carbon (EAC) in order to reduce the elevated load of toxic pollutants below the regulatory limits. It was evaluated the effect of increasing the amount of bioadsorbent as well as the influence of two successive adsorption cycles in the removal efficiency of pollutants. The most favourable sorption conditions onto CAB provided removal percentages of 85.02% for CNf and between 93.40–98.21% for heavy metals regarding the raw wastewater. The adsorption capacity of each pollutant onto CAB was considerably increased during the first 30 min of contact time, but after achieving the equilibrium, the following sorption capacities were obtained: 1177, 107.3, 39.5 and 1.52 mg/g for CNf, Ni, Cu and Zn, respectively. The kinetic adsorption of pollutants onto the CAB was adjusted to different kinetic models, observing that kinetic data agreed with the pseudo-second-order model. The information about intraparticle diffusion mechanisms in the bioadsorption process was also interpreted.
Highlights
Cyanide is cytotoxic for animals and humans, inhibiting the cytochrome oxidase enzyme and preventing the transport of oxygen into the cells [1]
It is important to highlight the elevated content of CNf quantified (51,190 mg/L), which is in good agreement with other plating baths previously analysed with values of 30,000 mg/L of CNTotal [13] or even ranging from
These limit values are 0.5 mg/L for CNf and 1 mg/L for CNTotal and, in the case of heavy metals (Ni, Cu and Zn), the limit values ranged from 2–3 mg/L depending on the element
Summary
Cyanide is cytotoxic for animals and humans, inhibiting the cytochrome oxidase enzyme and preventing the transport of oxygen into the cells [1]. Chronic exposure of humans and other living organisms to cyanide causes damage of central nervous system with cardiovascular and respiratory disorders as well as endocrine malfunctioning [2]. Cyanide is widely used in electroplating industries in order to assure the high quality of the finished products and, is a common contaminant in different industrial effluents including metal processing, gold mining, and plastics [3]. In wastewater, mainly exists in different chemical forms: Free cyanide and associated with metallic elements forming cyanide complexes. Free cyanide (CNf ) includes the most toxic forms: Cyanide anion (CN− ) and hydrogen cyanide (HCN). Weak and moderately strong cyanide-complexes refer to complexes such as Cd, Cu, Ni and Zn and strong cyanide-complexes include complexes such as Fe, Au and Co [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
