Lab scale investigations by Hindustan Zinc Limited (HZL) using a 3 " flotation column and data analysis by Engineers India Limited (EIL) confirmed amenability of production of zinc concentrate of desired grade by column flotation. Based on statistically designed pilot scale experiments, on-line data generated by HZL, the scale-up and design has been done using the software COLSIM developed at EIL. Two columns in series replaced nine conventional mechanical cells in three cleaning stages of the zinc circuit at Rajpura Dariba Mine (RD Mine) of HZL. The plant has been commissioned and has been in operation for over one year. The column flotation system has led to an improvement in final zinc concentrate grade by simultaneous reduction of the insoluble matters (ISM). (C) 2000