French Technological Development in Nodule Mining

ABSTRACT Since 1971, AFERNOD has studied mining concepts which are adapted to the requirements of commercial exploitation of the nodules deposits together with survey of nodule deposits and evaluations of metallurgical processing. Among several possibilities, AFERNOD has selected different potentially feasible concepts and has evaluated various systems in order to enable AFERNOD to determine their relative interest in relation to:the probable mine sites characteristicsthe technical feasibility i.e. the existing gaps between available deep sea technology and the technical specifications imposed to meet commercial requirements. The results of these studies have supplied AFERNOD with reference and allowed an approach of the financial risks involved with the various mining systems considered. INTRODUCTION Beside the economics and the juridical aspects, the collection of nodules and the lifting of the ore to the ocean surface have been claimed to be the most technically difficult problem raised in the evaluation of commercial nodule mining. For several years the French Group AFERNOD has been evaluating three potentially concepts for nodule mining :–First, the continuous line bucket (CLB) which is a mechanical mining device with a long rotating loop of synthetic fiber rope and buckets, suspended from a support,–Secondly, the so-called "hydraulic" concept involving nodule bottom collector feeding a string of lifting pipe hung to the mining vessel,–and thirdly, a series of remote controlled mining shuttles moving between the ocean floor and a mining platform. The comparaison of the merits of the three systems with respect to the constrains imposed both by the characteristics of the mining site and the requirements which have to be met for commercial operation has enabled AFERNOD to orient its research and development efforts and its general policy. MINING SITE CHARACTERISTICS The main parameters to be considered when comparing the merits of mining systems are:–First, the nodule concentration (i.e. the abundance of nodule per surface unit) and the variation of this parameter within the mining zone,–Secondly, the bathymetry of the site and the obstructions occurence on the seafloor,–Thirdly, the nature and mechanical properties of the sediment supporting the nodules,–and finally, the weather and currents conditions. The selection of a mining site requires the presence of nodules of sufficient grade and concentration. Available data show that homogeneous nodule grade can be found in large area and that an average concentration of 10 Kg per square meter is realistic. Nevertheless, the distribution of nodules on the sea floor may present large variations and the mining system will have to accomodate large fluctuations in the flow of collected ore and still maintain nominal production rate. Furthermore, the capability for a mining system to achieve nominal production rate on a mining zone with lower average concentration value, increases considerably the total tonnage of recoverable ore. Indeed, AFERNOD exploration data indicate that lowering the cut-off concentration from 10 to 5 Kg per square meter might increase the recoverable estimated tonnage of nodules (2.5 % Ni + Cu) by a factor of ten.