In response to Mr. Hernesma’s letter in last week’s Timberjay, I have been researching the copper-nickel sulfide mining issue for twenty years. The following was sent to me by an eminent and respected scientist.
“The folks who talk about low sulfide ore content are using the ‘game of units’ to try to minimize the potential for impacts by the reactive component– sulfide expressed in percentages. While the potential impacts for significant water concentration changes are at water concentration units of parts per billion, or percent changes of 0.000000001 percent expressed in terms of weight of water.
By expressing the concentration of sulfide as a percentage, by weight, in the ore or ore tailings, the values computed are made to appear small, but in reality, they are not insignificant!
Try expressing the “low sulfide ore” concentrations in parts per million or parts per billion, and you will get a better idea of the “impact potential” for making changes in water concentrations for precipitation percolating through an unprotected pile of waste rock or sulfide ore tailings containing 0.1 percent sulfide (0.1 percent = 1/1000 = 1,000/1,000,000 or one thousand parts per million!).
Consider the following simplified, hypothetical calculation: a sample containing 0.1 percent sulfide ore was contained in a box of one cubic decimeter in size, was air oxidized, followed by leaching with the same volume of water such that 1 percent of the sulfide resulted in acid sulfate dissolved. The amount of acid, in water, would be approximately 10 parts per million and the pH of the water would be about 5.0. If 10 percent of the sulfide leached, the water pH would be about 4. (The actual amounts of acid would be higher (by 3x) due to the difference in density between ore and water.) As for impacts, most freshwater aquatic life cannot tolerate water pH below 4.
And this hypothetical calculation is just for the acid content, and is only the beginning of what happens as the metal content of the ore dissolves in low pH water giving toxic concentrations of heavy metals including aluminum, to aquatic life.”
Carla Arneson
Ely