A1 Journal article (refereed), original research

Treatment of mining wastewater polluted with cyanide by coagulation processes: A mechanistic study


Open Access publication

Publication Details
Authors: Mamelkina Maria A., Herraiz-Carboné Miguel, Cotillas Salvador, Lacasa Engracia, Sáez Cristina, Tuunila Ritva, Sillanpää Mika, Häkkinen Antti, Rodrigo Manuel A.
Publisher: Elsevier
Publication year: 2019
Language: English
Related Journal or Series Information: Separation and Purification Technology
ISSN: 1383-5866
eISSN: 1873-3794
JUFO-Level of this publication: 2
Open Access: Open Access publication
Location of the parallel saved publication: http://urn.fi/URN:NBN:fi-fe202001283714

Abstract

In this work, coagulation and electrocoagulation for the removal of
cyanide ions contained in synthetic mining wastewater were evaluated
paying particular attention to the elucidation of the coagulation
mechanisms. Iron and aluminum salts with concentrations ranging from
0.01 to 10 000 mg dm−3 metal were used in chemical
coagulation. Experimental data were properly fitted to Freundlich
isotherm to elucidate that the main mechanism to remove cyanide during
chemical coagulation was adsorption onto coagulant flocs although a
maximum cyanide removal percentage of only 25% was attained. Then,
electrochemical coagulation with iron and aluminum electrodes was
evaluated at 1, 10 and 100 A m−2, obtaining completely
different results. Iron electrochemical coagulation leads to the
complete cyanide removal regardless of the current density applied,
although the TOC removal was much lower than expected. On the contrary,
only 60% of cyanide removal was reached by aluminum electrochemical
coagulation and its efficiency was found to be highly dependent on the
current density applied. Furthermore, no cyanate or hazardous inorganic
chlorine species were detected during both electrocoagulation processes.
However, chloride was oxidized to hypochlorite and then, it reacted
with ammonium ions (contained in mining wastewater or produced by
chemical reduction of nitrate by aluminum) to form chloramines. A
proposal of coagulation mechanisms during the electrochemical process
that explains experimental results was developed which involved the
formation of iron-cyanide complexes, charge neutralization, adsorption
on a superficially charged metal precipitate and/or enmeshment into a
sweep metal floc.


Last updated on 2020-20-03 at 10:03