This is an important question because it determines what type of technology(ies) will be necessary to recover the target metal.  Higher metal concentrations, greater than 10 g/L, are typically amenable to plating to produce a high purity metal plate.  Lower metal concentrations, typically in the 1-5 g/L range, can be used to produce an electrolytic powder.  Below 1 g/L, a high surface area cathode is required to recover low concentration metals via electrowinning.  In some cases, a combination of electrowinning technologies can be used to recover, concentrate, plate and/or polish an electrolyte in order to recover the target metal.  In other cases, pre-concentration with ion exchange (IX) or solvent extraction (SX) may be required prior to electrowinning.