An OK100 tank cell flotation unit is installed in the zinc circuit of the Pasminco concentrator at Broken Hill, The unit has been in service as a zinc rougher unit since May 1994, and this paper details the operational and research experiences to date with the tank cell. The OK100 rank cell installed in the Broken Hill concentrator zinc circuit is relatively taller and thinner than the current commercial version, with a similar volume. The unit utilises the conventional Outokumpu multi-mit mechanism, but is a deeper cell with an adjustable froth crowder (booster cone). The unit is equipped with baffles which serve to reduce the rotational vector associated with the rotor. The OK100 rank cell is a 104 cubic metre flotation unit with a single rotor/stator assembly. The cell was retrafitted from an existing surplus to requirements conditioner. The tank cell operates in a manner that is similar to a flotation column and has been termed a ＇＇virtual＇＇ column try Outokumpu, due to considerations with respect to kinetics and flotation surface area being able to be altered depending on plant operating conditions. A series of studies have been made on the OK100 characterising superficial gas velocity, air hold up, bubble size, carrying rate, flotation kinetics, residence time, mass flow grade, recovery relationships at various operating parameters of cone height, froth depth and airflow rates. Measurements of Jg and air hold up will be detailed. Also a description of operating and maintenance issues will be presented.