Normally we will use around 32% HCl (molarity 10.2), with some heat it is possible to use a somewhat more dilute solution, the leach would concentrate as heated, heating the solution can be a double edged sword, heat would drive off chlorine gas you need in solution, which could cause you to use more hypochlorite, which can also neutralize acid with more additions of the basic solution, but heat can also be helpful when trying to get the PGM's into solution, so it is somewhat of a balancing act when using heat.
