190

13 Biosorption of Heavy Metals and Metal-Complexed Dyes Under the Influence

system leading to massive health issues for both aquatic species and human beings

through the food chain and reduces the photosynthetic activity of the plants. In addi-

tion to that, the anionic dyes used in wool, polyamide and polypropylene fibers, and

cationic dyes which are highly water-soluble and reactive dyes pose harmful effects

such as skin allergies, irritation on skins, mutation of genes, tumors, and cancer

diseases [4].

Ozacar and Sengil [5] revealed that the negatively charged (anionic) metal col-

orants are mostly used in fabric and tanning industries, and polyamide fibers are

used to reduce the fading of pigments. The major metals used for producing met-

alized dyes are copper, cobalt, and chromium. Moreover, the complexed dyes and

metal ions lead to the formation of several color shades of dyes. Additionally, the

salt-based metal-complexed dyes are mainly used in the dye and finishing industries

to reduce the dissolution of dye and enhance the aggregation of the dye molecules.

In this process, NaCl is the major salt used as an additive in the dying process which

affects the aquatic species when the salt concentration is high in the system.

Heavy metals and dyes become more toxic and cause detrimental effects on the

environment when their concentration exceeds the permissible limit in the efflu-

ents. To overcome these issues, many conventional methods have been applied to

remediate deadly heavy metals and dyes from the industrial run-offs. One method

is chemical precipitation where alkylation of metal solution by the coagulants such

as sodium bisulfide, potash alum, sulfide, iron base salts, and limestone will be car-

ried out to convert solubilized metal ions into insoluble forms. Electrowinning is

another method where recuperation of metals from mining, metallurgical operation,

electrical industries, and electronics will be carried out. This process is carried out

by passing current from an inert anode to a cathode kept in an electrolyte, which

contains metal ions and follows an electroplating process. Reverse osmosis is yet

another conventional method to retentate the heavy metals using a semipermeable

membrane. The membrane-based process has the advantage for the selective metal

separation and highly stable with respect to changes in pH [6].

Two-phase extraction method is another viable method to recuperate selective

metals (for example, platinum group metals from spent catalysts). The extractants

used to recover the metal ions are organophosphorus compounds, aliphatic amines,

and quaternary ammonium salts. But this extraction process is very difficult to con-

valescence metals from the organic phase, and also the harmfulness of extractants

is determinantal factor in this separation process. However, these methods are most

expensive and are not preferable for environmental conditions. Gupta et al. [7] stated

that surface adsorption is one of the mass transfer processes for an active elimination

of dyes compared to other processes. Zeolite, polymer-based porous material, and

activated carbons are the selective adsorbents which are used to remediate the dyes

because of their huge surface area to volume ratio and the presence of functional

groups present on the surface of the zeolite. In this chapter, we have mainly concen-

trated on discussing the importance of biosorption for removing metal-complexed

dyes while using various microbial species such as bacteria, fungi, or yeast and also

the new methods which were adopted in industrial processes.