Exploring Froth Flotation & Negative Energy of Activation

[Evil]

does anyone here has any idea what is froth flotation(in extraction pf metals) and negative energy of activation( as in chemical energetics)?
thanks for any input.

 

[Gokul43201]

Froth flotation is an ore concentration technique commonly used with (hydrophobic)sulfide ores (such as iron or copper pyrites). Crude ore is ground to a fine powder and mixed with water, frothing reagents, and collecting reagents. When air is blown through the mixture, mineral particles cling to the bubbles, which rise to form a froth on the surface. The waste material (gangue) settles to the bottom. The froth is skimmed off, and the water and chemicals are distilled or otherwise removed, leaving a clean concentrate.

For more discussion, see http://www.engr.pitt.edu/chemical/undergrad/lab_manuals/flotation.pdf

 

[Gokul43201]

Negative Activation is only an apparent effect, it is not a real quantity. Very rarely, in reactions that go through some kind of intermediate, the reaction rate is found to be dependent on the equilibrium constant of the rate determining step. If this step is exothermic, the equilibrium constant decreases with increasing temperature. So, even though the rate constant increases with increasing temperature (as it should - this is a sign of positive activation energy), the product of the rate constant and equilibrium constant (or apparent rate constant) may be decreasing with increasing temperature. This is what is referred to as negative activation.

The oxidation of NO to give NO2 is such a reaction.

See : http://www.rod.beavon.clara.net/nitrogenmonoxide.htm