In Mond’s process for refining nickel metal Nickel is heated in a stream of carbon monoxide forming a volatile complex , the complex is subjected to higher temperature so that it is decomposed giving the pure metal.$Ni+xCO\stackrel{yk-zk}{\to }Ni{\left(CO\right)}_x$

$Ni{\left(CO\right)}_x\stackrel{mk-nk}{\to }Ni+XCO$