Based on the laboratory work, poly-metallic nodules pilot plant of 500 kg per day processing capacity was designed and set up at Hindustan Zinc Limited, Udaipur (India). The process is based on the reductive pressure leaching of nodules using sulfur dioxide as reducing agent in the presence of ammonia. The experiments conducted in the pilot plant show an average recovery for copper, nickel and cobalt as 85%, 90% and 80% respectively. The paper presents the highlights of the process along with the pilot plant description. Some of the selected results are also discussed. (C) 2003 Elsevier Ltd. All rights reserved.