The effect of chloride and sulfate on the mineralogy and morphology of synthetically precipitated copper solids

Date of Award

2013

Degree Name

M.S. in Civil Engineering

Department

Department of Civil and Environmental Engineering and Engineering Mechanics

Advisor/Chair

Advisor: Denise Taylor

Abstract

Since the implementation of the Lead and Copper Rule in 1991, multiple studies have been completed to explain, predict and mitigate the problems of copper corrosion. Water chemistry is a leading factor in initiating corrosion and a number of parameters have been postulated to be responsible, including pH, alkalinity, chloride and sulfate. The purpose of this research is to identify aqueous conditions that support the formation of copper corrosion by-products found in distribution systems. Specifically, this work attempted to understand: 1) the role of aggressive ions, chloride and sulfate, in the formation synthetically precipitated particles; 2) the effect of aging on solubility and morphology; 3) evaluate morphology associated with solids. Precipitation experiments were conducted at pH seven and nine, with varied dissolved inorganic carbon (10, 50 mg C/L), and ratios of chloride and sulfate at 1:1, 5:1 and 1:5. Copper was added as cupric perchlorate solution at a concentration of 15 mg/L. Analysis of solubility, mineralogy, and morphological changes were conducted over three months using induced coupled argon plasma spectrometry, x-ray diffraction and scanning electron microscope. This research generally supports results previously reported in literature: high pH conditions over a range of DIC levels favor the formation of tenorite. High DIC, neutral pH water favors formation of malachite and experience higher solubility levels. The effect of chloride and sulfate was most evident at low pH, low DIC conditions where connellite, langite and an unidentified mineral were formed. The effect of aging was evident through x-ray diffraction as particles transitioned from amorphous to slightly crystalline. This transition was most evident within 28 days of precipitation, which also correlated to a reduction in solubility. Microscopy analysis provided confirmation on the morphology habits associated with tenorite, malachite, connellite and langite. In additional tenorite and malachite were compared to scale from distribution systems and were comparable in surface features, size and habit.

Keywords

Copper Corrosion, Copper Morphology, Chlorides, Sulfates, Water chemistry, Civil Engineering; copper corrosion; water chemistry; chloride and sulfate; x-ray diffraction; scanning electron microscopy

Rights Statement

Copyright © 2013, author

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