Zinc Solubility

A. Hi,

I believe you want the solubility of zinc in water.

There is no single value -- the solubility depends upon the properties of the water. For example, the solubility increases as acidity increases (also known as lowering of pH), temperature increases, chlorine concentration increases and hardness decreases.

However, for ordinary water, the solubility of zinc is often limited by how much can dissolve before zinc hydroxide forms. From the solubility product, Ksp, for zinc hydroxide Zn(OH)2, and the pH value of the water, the solubility of zinc can be calculated. At room temperature, a water with pH = 7 (neutral) will have a dissolved zinc concentration, Zn(+2), of 0.29 grams per Liter = 290 ppm (parts per million, by weight) = 0.039 oz. (wt.) per gallon. If the pH increases to 8, the solubility decreases by a factor of 100, to 2.9 ppm. A chart showing Zn solubility at different pH values is at www.finishing.com/library/metalpH.html The solubility values shown on this chart are lower than those calculated above because they were measured for hard water containing several dissolved metals.

It may also be of interest that a small amount of Zn is present in natural waters. "Zinc is present in most rocks and in certain minerals. As these materials break down over time, zinc may be released to surface water or groundwater. This source of zinc is diluted and widely dispersed. Rainwater in urban areas, mine drainage, and municipal and industrial wastes are more concentrated sources of zinc in water." ---FACT FLASH 9: Common Contaminants, U.S. EPA.

A. Hi, Adel. There is currently an excellent page on line at
www.chem.purdue.edu/gchelp/howtosolveit/equilibrium/solubility_products.htm#Solubilitycommonion br> which gives the calculations and examples.

This subject is dry for most readers (like me!), so you'll probably get a more enthusiastic response if you can lift the veil of tedium by describing the real-world situation you find yourself in that is requiring you to run such calculations. Good luck!

Regards,

Thanks for the graph on metals solubility vs. pH. Was very helpful at a customer site today to explain why it was best to reduce the pH (which was at 11.5) in order to improve Zn precipitation. A picture is worth a thousand words and the graph explained it better than saying "Zinc is amphoteric"! The fact that solubility can go back up as you increase the pH is a surprise to some.