I recently did a reagent plant trial and worked with a pretty nice flotation reagent metering pumps.  The pump is supplied by http://www.pmps.co.za

This portable reagent supply unit is a mechanical diaphragm metering pump.  As see on http://www.pmps.co.za/obl-mechanical-diaphragm-dosing-pump

They even had “Water Driven Pumps”

Other pumps I never worked with include http://www.awe-ltd.co.uk/products/dosing_pumps_electronic.html and http://www.lutzjescoamerica.com/index.php?id=1645

Also https://www.911metallurgist.com/blog/mibc-frother-pump