The Effect of Water Chemistry on the Solubility and Properties of Freshly Precipitated Copper Solids
High levels of copper in tap water may cause acute health problems. The EPA Lead and Copper Rule (LCR) set a copper action level of 1.3 mg/L in a 1-liter, first-draw sample collected from the consumer’s tap. Knowing the effect of water chemistry on copper solubility will help water utilities and engineers reduce copper levels at the consumer’s tap.
A great deal of research has been conducted on:
- copper corrosion and
- the leaching of copper from drinking water distribution system materials.
EPA researchers are study the effects of water chemistry on the solubility and properties of newly precipitated copper(II) , aka Cu(II), solids. The following were investigated:
- dissolved inorganic carbon (DIC),
- electrophoretic mobility and
Test water at the desired water quality level was used. A computer software-controlled dual titrator system was used to maintain a constant pH. It would rapidly add small increments of acid or base to offset pH changes caused by the addition of copper and chemical reactions. The computer software recorded pH values and titrant volumes. Copper was added to the water and allowed to precipitate for a predetermined amount of time. Then the water was filtered through a 0.2 µm-filter to separate particulate from soluble copper. Particle analysis was conducted on filtered solids or copper particle suspensions.
Results and Impacts (to Date)
The key findings of this study revealed that:
- Increasing the pH and concentration of orthophosphate caused a decrease in Cu(II) solubility.
- Increasing the concentration of DIC increased Cu(II) solubility.
- Increasing the concentration of sulfate had no effect on copper solubility.
- Silicate and polyphosphate affected the surface charge and stability of copper particles.
Figure 1 shows the effect of pH and DIC on copper solubility at 23 degrees Celsius. Precipitation experiment data were compared to theoretical solubility model predictions. The model was modified to produce a “best fit.”
The findings listed above are consistent with Cu(II) solubility models and provide the most practical method to date for researchers to recommend water treatment for utilities.
Darren Lytle (513) 569-7432,