Elimination of harmful substances in the sulfur dyeing
process
The major harmful substances in the sulfur dyeing process include
conventional reducing agents such as sodium sulfide and
oxidizing agents such as dichromate, hydrogen peroxide, and sodium
hypochlorite. Sodium dithionate, thiourea dioxide, and indirect
cathodic reduction have been studied and tested as
replacements for sodium sulfide [101]. They are still not commonly
used in the textile industry because of their inconsistent results
and higher cost. Glucose, an eco-friendly reducing agent, has been
chosen for the replacement of sodium sulfide in textile processes
for dyeing with sulfur dyes and for the bleaching of cotton fabrics
[102,103]. Employing this new reducing agent has shown better
quality effluent and comparable results in terms of color strength
and washing fastness without any significant loss in tensile
strength relative to sodium sulfide [101]. This reducing sugar has
an optimal concentration based on its redox potential, which results
in a maximum dye uptake with less color loss. This redox potential
is affected by magnetization [102]. The magnetic treatment
promises some technological and economical benefits for textile
technologies. This treatment enhances both the reducing ability
of glucose and the oxidation ability of hydrogen peroxide and sodium
hypochlorite. In the dyeing of cotton with sulfur dyes, the
application of dichromate develops stiffness in dyed cotton due
to the precipitation of chromium compounds, causing an occasional
change in tone and an increase in the solid content of the
discharged waste water [74]. Laccase has been studied as a potential
oxidizing catalyst for the oxidation of sulfur-dyed cotton in an
attempt to substitute for toxic dichromate.