4.2.4. Fertilizer industry waste
Fertilizer industry also produces a number of by-products in large quantities which create serious disposal problems and degrade the surrounding environment. Fe(III)/Cr(III) hydroxide, a waste material from the fertilizer industry has been used by Namasivayam and Ranganthan for the adsorption of Cr(VI) from aqueous solution. The adsorption data fitted with both Freundlich and Langmuir models. Namasivayam and Senthilkumar investigated the potential of Fe(III)/Cr(III) hydroxide waste for the removal of As(V). Adsorption was explained by considering zero-point of charge (ZPC) of the adsorbent material. The pHzpc of waste Fe(III)/Cr(III) hydroxide was 8.3. In the pH range 3 –7, H2AsO4− was predominantly adsorbed. The adsorbent acquired positive charge in this pH range and adsorption was facilitated by coulombic interactions. In the pH range 7–10, specific interactions occurred, since dissociation of arsenic acid is expected. The transfer of a proton to the hydroxyl groups of the Fe(III)/Cr(III) hydroxide surface is also possible. A surface complexation model was proposed for As(V) adsorption on Fe(III)/Cr(VI) waste.