Abstract

In this work, the performance of phosphonates as ferric (Fe3+) ions stabilization and iron oxide (Fe2O3) dispersing agents for aqueous system has been investigated. The phosphonates tested include: 2-hydroxyphosphono acetic acid (HPA), 1-hydroxyethylidine 1,1-diphosphonic acid (HEDP), aminotris (methylene phosphonic acid) (AMP), 2-phosphono-butane 1,2,4-tricarboxylic acid (PBTC), and polyamino polyether methylene phosphonic acid (PAPEMP). Results suggest that performance of phosphonates strongly depends on several factors including phosphonate concentration, reaction time, and phosphonate architecture. Comparative performance data on poly(acrylic acid) and terpolymer of acrylic acid: 2-acrylamido-2-methyl propane sulfonic acid: sulfonated styrene is also discussed.

Introduction

Among the various dissolved impurities present in the natural waters, metal ions including aluminum, copper, iron, manganese, and zinc when present at low concentrations (e.g., few milligrams per liter, mg/L) pose the most serious problems in many domestic and industrial applications. These metal ions will not only form insoluble hydroxides under acid and/or alkaline pH conditions and deposit on equipment surfaces but will also influence the performance of scale inhibitors and dispersants commonly used in water treatment formulations.1,2 Removal of heavy metals from industrial wastewater is of primary importance because they are not only causing contamination of water bodies but are also toxic to many life forms. 3 Industrial processes such as paint manufacturing, printed circuit board manufacturing, metal polishing, and wood preservatives generate wastewater containing heavy metal contaminants. Because most heavy metals are non-degradable into nontoxic end products, their concentrations must be reduced to acceptable levels before discharging them into environment. Otherwise, these could pose threats to public health and/or affect the aesthetic quality of potable water. Over the years, various methods have been developed to remove toxic metals from aqueous streams. These approaches include precipitation, ion exchange, coagulation, adsorption, and membrane-based filtration processes.

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