**1. Introduction**

Remediation of environmental sources is a very important concern for human beings since these are essential to sustain life [1]. The presence of heavy metal ions in the environment is becoming a serious threat to public health and the environment. Heavy metal contamination exists in aqueous wastes of many industries, such as metal plating, mining operations, tanneries, chlor-alkali, radiator manufacturing, smelting, alloy industries and storage battery manufacture [2]. Most of the heavy metals are toxic, and therefore, their removal from environmental sources is very important [3]. Several methods can be used for the removal of metal ions from water including chemical precipitation, ion exchange, filtration, reverse osmosis,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

adsorption and membrane separation [4]. The advantages and the disadvantages of the various treatment processes used in heavy metal removal are given in **Table 1** [5].

By far, the most widely used method for removing heavy metals from solution is chemical precipitation. The soluble metal is converted into an insoluble precipitate (i.e. its hydroxide) by the increase in the pH of the solution. It is relatively simple and inexpensive to operate. The precipitates can be separated from the water by sedimentation or filtration. The treated water was then decanted and appropriately discharged or reused. The conventional chemical precipitation processes include hydroxide precipitation and sulphide precipitation [5].

Ion exchange is another most widely used method for the removal of heavy metals from the solution [6]. The ion exchanger is a solid capable of exchanging either cations or anions from the surrounding materials. Commonly used matrices for ion exchange are synthetic organic ion exchange resins.

Coagulation-flocculation can also be employed to treat water with heavy metals, wherein the coagulation process destabilises colloidal particles by adding a chemical agent (coagulant) and results in sedimentation [7]. Many coagulants are widely used in the conventional wastewater treatment processes such as aluminium, ferrous sulphate and ferric chloride, resulting in the effective removal of wastewater particulates and impurities by charge neutralisation of particles and by enmeshment of the impurities on the formed amorphous metal hydroxide precipitates. Coagulation is followed by flocculation of the unstable particles in order to increase their size and form into bulky floccules which can be settled out. Today, many kinds of flocculants, such as polyaluminium chloride, polyferric sulphate and polyacrylamide (PAM), are widely used in the treatment of waste water. However, it is nearly impracticable to remove heavy metals very well from waste water directly by these current flocculants.

Flotation is employed to separate solids or dispersed liquids from a liquid phase using bubble attachment [8]. Adsorptive bubble separation employs foaming to separate the metal impurities. Ion flotation, precipitate flotation and sorptive flotation are the main flotation process mechanisms for removal of metal ions from solution. Membrane filtration has received considerable attention for the treatment of inorganic effluent, since it is capable of removing not only suspended solid and organic compounds but also inorganic contaminants such as heavy metals.

Electrochemical methods involve the plating out of metal ions on a cathode surface and can recover metals in the elemental metal state. Electrochemical wastewater technologies involve relatively large capital investment and the expensive electricity supply. The cost factor prevents the usage of this method to be widely applied industrially [9].

Adsorption is now recognised as an effective and economic method for heavy metal wastewater treatment. The adsorption process offers flexibility in design and operation and in many cases will produce high-quality treated effluent. Among these methods, adsorption via the use of adsorbent is one of the most effective methods since it is rapid, economic, effective and easy. In addition, the regeneration of the adsorbent with resultant economy of operation may be possible because adsorption is sometimes reversible [10].


**Table 1.** Comparison of treatment processes used for heavy metal removal.

adsorption and membrane separation [4]. The advantages and the disadvantages of the vari-

By far, the most widely used method for removing heavy metals from solution is chemical precipitation. The soluble metal is converted into an insoluble precipitate (i.e. its hydroxide) by the increase in the pH of the solution. It is relatively simple and inexpensive to operate. The precipitates can be separated from the water by sedimentation or filtration. The treated water was then decanted and appropriately discharged or reused. The conventional chemical precipitation processes include hydroxide precipitation and sulphide precipitation [5].

Ion exchange is another most widely used method for the removal of heavy metals from the solution [6]. The ion exchanger is a solid capable of exchanging either cations or anions from the surrounding materials. Commonly used matrices for ion exchange are synthetic organic

Coagulation-flocculation can also be employed to treat water with heavy metals, wherein the coagulation process destabilises colloidal particles by adding a chemical agent (coagulant) and results in sedimentation [7]. Many coagulants are widely used in the conventional wastewater treatment processes such as aluminium, ferrous sulphate and ferric chloride, resulting in the effective removal of wastewater particulates and impurities by charge neutralisation of particles and by enmeshment of the impurities on the formed amorphous metal hydroxide precipitates. Coagulation is followed by flocculation of the unstable particles in order to increase their size and form into bulky floccules which can be settled out. Today, many kinds of flocculants, such as polyaluminium chloride, polyferric sulphate and polyacrylamide (PAM), are widely used in the treatment of waste water. However, it is nearly impracticable to remove heavy metals very well from waste water directly by these current

Flotation is employed to separate solids or dispersed liquids from a liquid phase using bubble attachment [8]. Adsorptive bubble separation employs foaming to separate the metal impurities. Ion flotation, precipitate flotation and sorptive flotation are the main flotation process mechanisms for removal of metal ions from solution. Membrane filtration has received considerable attention for the treatment of inorganic effluent, since it is capable of removing not only suspended solid and organic compounds but also inorganic contaminants such as heavy

Electrochemical methods involve the plating out of metal ions on a cathode surface and can recover metals in the elemental metal state. Electrochemical wastewater technologies involve relatively large capital investment and the expensive electricity supply. The cost factor pre-

Adsorption is now recognised as an effective and economic method for heavy metal wastewater treatment. The adsorption process offers flexibility in design and operation and in many cases will produce high-quality treated effluent. Among these methods, adsorption via the use of adsorbent is one of the most effective methods since it is rapid, economic, effective and easy. In addition, the regeneration of the adsorbent with resultant economy of operation may

vents the usage of this method to be widely applied industrially [9].

be possible because adsorption is sometimes reversible [10].

ous treatment processes used in heavy metal removal are given in **Table 1** [5].

ion exchange resins.

176 Acrylic Polymers in Healthcare

flocculants.

metals.

In recent years, polymeric adsorbents have received considerable interest for heavy metal removal mainly due to important properties such as easy synthesis at controlled dimensions with variable functional groups, perfect mechanical rigidity, tunable surface chemistry, large surface area, pore size distribution, high uptake values and feasible regeneration under mild conditions. These novel properties allow the polymeric adsorbent to be applied for use in drug delivery systems, optics and water treatment. These can also be incorporated with other particles making them extremely versatile [11].
