Selective Removal of Toxic Metals like Copper and Arsenic from Drinking Water Using Phenol‐Formaldehyde Type Chelating Resins

Abstract

The concentration of different toxic metals has increased beyond environmentally and ecologically permissible levels due to the increase in industrial activity. More than 100 million people of Bangladesh and West Bengal in India are affected by drinking ground water contaminated with arsenic and some parts of India is also affected by poisoning effect of copper, cadmium and fluoride. Different methods have been evolved to reduce the arsenic concentration in drinking water to a maximum permissible level of 10 μg/L where as various methods are also available to separate copper from drinking water. Of the proven methods available today, removal of arsenic by polymeric ion exchangers has been most effective. While chelating ion exchange resins having specific chelating groups attached to a polymer have found extensive use in sorption and pre concentration of Cu2+ions. Both the methods are coupled here to separate and preconcentrate toxic metal cation Cu2+and metal anion arsenate(AsO4–) at the same time. We have prepared a series of low-cost polymeric resins, which are very efficient in removing copper ion from drinking water and after coordinating with copper ion they act as polymeric ligand exchanger, which are efficiently removing arsenate from drinking water. For this purpose Schiff bases were prepared by condensingo-phenylenediamine witho-,m-, andp-hydroxybenzaldehydes. Condensing these phenolic Schiff bases with formaldehyde afforded the chelating resins in high yields. These resins are loaded with Cu2+, Ni2+2+, and Fe3+ions. The resins and the polychelates are highly insoluble in water. In powdered form the metal ion-loaded resins are found to very efficiently remove arsenate ion from water at neutral pH. Resins loaded with optimum amount of Cu2+ion is more effective in removing arsenate ions compared to those with Fe3+ion, apparently because Cu2+is a stronger Lewis acid than Fe3+. Various parameters influencing the removal of the arsenate ion from drinking water to a concentration level below 20 μg/L are studied.

Exploring the Mechanisms of Selectivity for Environmentally Significant Oxo-Anion Removal during Water Treatment: A Review of Common Competing Oxo-Anions and Tools for Quantifying Selective Adsorption

“…Henry et al developed a Cu­(II)–PLE that selected (measured by ∝) for arsenate and phosphate over sulfate; however, it failed to separate the most difficult competitive pair, arsenate and phosphate. Similar Cu­(II)–PLEs were selective (measured by ∝) for arsenate and selenite over weakly competing bicarbonate and sulfate, ,,, and perchlorate over sulfate . However, strongly competitive phosphate was not evaluated.…”

Synthesis of a novolac‐based 3‐aminopropylsiloxane resin and its application for the removal of Cu2+, Cr3+, and Ni2+ from electroplating wastewater

“…The obtained capacity of PF‐APS is relatively high compared with the reported PF‐based ion exchangers; PF‐functionalized with sulfonic and carboxylic acids has metal capacities of 0.058–0.18 mEq g −1 . PF‐Schiff bases showed Cu 2+ capacity of 0.232–0.315 mEq g −1 . This is an important indication of obtaining a highly activated ion exchanger.…”

“…Condensing these phenolic Schiff bases with formaldehyde affords the chelating resins in high yields. These resins are loaded with Cu 2+ , Ni 2+ , and Fe 3+ ions with equilibration time 24 h . Samal et al reported the synthesis of chelating resins by condensing a phenolic Schiff base derived from 4,4′‐diaminodiphenylmethane and o ‐hydroxyacetophenone with formaldehyde or furfuraldehyde.…”

Removal of Cu(II) Ions by Leucaena Leucocephala (Subabul) Seed Pods from Aqueous Solutions

“…One of the more important toxic metals, copper, finds its way to the water stream from industries like electroplating, mining, electrical and electronics, iron and steel production, the non-ferrous metal industry, the printing and photographic industries and metalworking and finishing processes. The adverse health effects caused by copper, mercury and arsenic poisoning are far more catastrophic than any other natural calamity through out the world in recent times 1 . Copper is not acutely toxic to humans, but its extensive use and increasing levels in the environment may cause serious health problems with prolonged exposure 2 .…”