Application of Sustainable and Low-Cost Sludge-Based Adsorbents …
43
2 were in the order of landfill sludge (159.0 ± 6.0 mgg
−1 ) > sewage sludge (114.7 ±
4.7 mgg
−1 ) > digested sludge (86.8 ± 4.5 mgg
−1 ) > waterworks sludge (47.0 ± 5.8
mgg
−1 ). The dye uptake by the landfill sludge was maintained at a significant level,
even at pH is higher than 7 compared to the other sludges.
2.5.7 Industrial Sludge as Adsorbents
Chromium Hydroxide Sludge
The sludge precipitates containing chromium hydroxide have shown good adsorptive
capacity in the removal of cationic, anionic and disperse dyes. The performance was
high at low pH for anion dyes (Reactive Blue and Congo red) and at high pH for
methylene blue with zero point surface charge as 10.5 [15]. The monolayer adsorption
at the surface of the negatively charged dye species to the positively charged surface
of the sludge precipitates through electrostatic attraction and followed first-order
reaction.
Metal Hydroxide Sludge
Studies of waste metal hydroxide sludge from electroplating industry are well suited
in the removal of reactive dyes [86, 88], catechol [87]. Adsorption capacity of metal
hydroxide sludge generally varied from 44 to 60 mg/g for reactive dyes [88]. High
capacity, low-cost adsorbents are still under development to reduce the adsorbent
dose and minimize disposal problems. The amphoteric behaviour of the hydroxide
sludge by the pH zpc determination was shown by the decrease in pH due to −OH
adsorption [104]. Particle size distribution and determination, physical textural properties and metal mobility under different pH conditions of the metal sludge were also
characterized. The X-ray fluorescence (XRF) showed the presence of mesopores
and macropores with an average pore diameter of 32.3 nm. High values of porosity
(>50%) were achieved, and possible agglomeration of finer particles in the waste
sludge created intraparticle spaces. A homogeneous solid diffusion model (HSDM)
was developed for homogenous particles, but has been applied to porous particles in
several adsorption systems [76, 113]. Equilibrium data were well described by both
Langmuir and Freundlich models. The maximum adsorption capacities obtained
varied between 275 mg/g (at 25 °C and pH4.0) and 21.9 mg/g (at 25 °C and pH10.0).
A decrease in adsorption capacity from 91.0 to 31.0 mg/g with decrease in pH was
studied with simulated textile effluents. The removal of three reactive dyes Reactive
Red 2, Reactive Dye 120 and Reactive Red 141 investigated using a metal hydroxide
sludge showed a reverse behaviour in the isothermal plot. The adsorption isotherm
including the Langmuir constants (Qo and b) and the Freundlich constants (K f ) for
Reactive Red 2 decreased with increasing temperature, but reversed for Reactive
43
2 were in the order of landfill sludge (159.0 ± 6.0 mgg
−1 ) > sewage sludge (114.7 ±
4.7 mgg
−1 ) > digested sludge (86.8 ± 4.5 mgg
−1 ) > waterworks sludge (47.0 ± 5.8
mgg
−1 ). The dye uptake by the landfill sludge was maintained at a significant level,
even at pH is higher than 7 compared to the other sludges.
2.5.7 Industrial Sludge as Adsorbents
Chromium Hydroxide Sludge
The sludge precipitates containing chromium hydroxide have shown good adsorptive
capacity in the removal of cationic, anionic and disperse dyes. The performance was
high at low pH for anion dyes (Reactive Blue and Congo red) and at high pH for
methylene blue with zero point surface charge as 10.5 [15]. The monolayer adsorption
at the surface of the negatively charged dye species to the positively charged surface
of the sludge precipitates through electrostatic attraction and followed first-order
reaction.
Metal Hydroxide Sludge
Studies of waste metal hydroxide sludge from electroplating industry are well suited
in the removal of reactive dyes [86, 88], catechol [87]. Adsorption capacity of metal
hydroxide sludge generally varied from 44 to 60 mg/g for reactive dyes [88]. High
capacity, low-cost adsorbents are still under development to reduce the adsorbent
dose and minimize disposal problems. The amphoteric behaviour of the hydroxide
sludge by the pH zpc determination was shown by the decrease in pH due to −OH
adsorption [104]. Particle size distribution and determination, physical textural properties and metal mobility under different pH conditions of the metal sludge were also
characterized. The X-ray fluorescence (XRF) showed the presence of mesopores
and macropores with an average pore diameter of 32.3 nm. High values of porosity
(>50%) were achieved, and possible agglomeration of finer particles in the waste
sludge created intraparticle spaces. A homogeneous solid diffusion model (HSDM)
was developed for homogenous particles, but has been applied to porous particles in
several adsorption systems [76, 113]. Equilibrium data were well described by both
Langmuir and Freundlich models. The maximum adsorption capacities obtained
varied between 275 mg/g (at 25 °C and pH4.0) and 21.9 mg/g (at 25 °C and pH10.0).
A decrease in adsorption capacity from 91.0 to 31.0 mg/g with decrease in pH was
studied with simulated textile effluents. The removal of three reactive dyes Reactive
Red 2, Reactive Dye 120 and Reactive Red 141 investigated using a metal hydroxide
sludge showed a reverse behaviour in the isothermal plot. The adsorption isotherm
including the Langmuir constants (Qo and b) and the Freundlich constants (K f ) for
Reactive Red 2 decreased with increasing temperature, but reversed for Reactive