Depends on what you're trying to achieve and process stream flow rate. Assuming you're dosing wastewater to suppress septicity? Last plant I did used variable speed diaphragm pumps to dose 40% w/w FeCL between 300 and 750 l/hr.
As with all coagulants, you really need to jar test for best results. Dosage is site specific. In some cases, the chemical supplier may be willing to perform these test for you through a field representative.
