It's not that it cements copper out of solution, it's that when it's saturated you have copper (I) chloride precipitate out of solution. And you are right, it does concentrate the values....but so much of modern e-waste is just flashed garbage. I have 500 lbs of pins that recover at 0.3g/lb, it's just not worthwhile to do anything to them except send them to the copper smelter as I can't CN strip them here.