With desalination becoming more common in some parts of the world I have wondered wether mineral extract from sea water could piggy back on this?

As the minerals are concentrated in the brine from desal plants would it not be more viable to attempt extraction from this water?

I think you'd have to consider details of the desalination method. My impression is that most desalination plants don't produce a very concentrated brine. You might have more luck recovering metals from evaporation ponds, such as those used for sea salt production for thousands of years.