Alternative Technology for Processing of Chromite and Laterite Ores: Crude Fe-Ni-Cr Alloy Production

Jeorgia G. Labador's picture
Submitted by Jeorgia G. Labador on February 16, 2015 - 3:15pm

Philippine deposits of chromite and nickeliferous laterite ores are among the largest in the world. Other metals like gold and copper have been processed into their metal form here in the Philippines, but nickel and chromium are usually exported in their raw form without adding value to the minerals.

Nickel and chromium are of vital importance to modern society. Without it, people would not be able to enjoy many of the things that they take for granted, such as computers, airplanes, and stainless steel appliances in homes and workplaces. The Philippines has laterite reserves of about 800 million tons and the biggest deposits are found in Palawan and Surigao. Chromite ore deposits are found in Northern Sierra Madre, Zambales, Samar, Eastern Mindanao, North Central Mindanao, Zamboanga Peninsula and Palawan.

At present, raw laterite and chromite ores are exported to Korea, Japan and China for processing. If we are going to add value to our mineral resources, putting up a processing plant to produce Fe-Ni-Cr-C alloy is strongly recommended. The traditional production of stainless steel involves melting together ferronickel, ferrochromium and pig iron in an electric arc furnace. The raw materials like ferronickel and ferrochromium were obtained by smelting laterite and chromite ores, respectively, in an electric arc furnace, while the pig iron is produced in the blast furnace after sintering the iron ore and coking the coal. The molten metal is then transferred to a refining vessel (argon-oxygen decarburization, AOD) to reduce the impurities, especially the carbon content, to a low level required in the final product.

Direct crude alloy production using raw laterite and chromite ores as iron, nickel and chromium source would have a significant reduction in total energy consumption. In view of the fact that traditional process use ferronickel, ferrochromium and pig iron/steel as feedstock to stainless steel making which contribute to the overall increase in total energy requirements. It is observed that the electricity consumption of the electric furnaces used in the production of ferronickel, ferrochromium and steel contributed approximately 50% to the total energy consumed in stainless steel production. Therefore, the direct processing of ores would have significant advantages compared to the traditional process of producing stainless steel as follows: 1) effective utilization of iron (Fe), nickel (Ni) and chromium (Cr) of the iron-rich laterite and chromite ores which are available locally; 2) the simplification of the process; and 3) the significant decrease in the total energy requirements for the direct stainless steel production.

The present proposal is designed to develop an alternative technology that will allow the nickel and chromium minerals to be value added. Potentially, it will lead to development of a new, more efficient technology for Fe-Cr-Ni-C alloy production from laterite and chromite ore, which is important to the metal industry and the Philippine economy. More fundamentally, it will provide insight on the mechanism of a liquid-liquid reaction between metal and slag.

This proposed alternative technology may also involve pre-reduction of iron oxides in laterite and chromite ores to iron carbide using gaseous hydrocarbon (methane or natural gas) before smelting. The iron carbide produced by the process may be used to produce the Fe-Ni-Cr alloy, for example, by smelting of metal carbide, or directly used in stainless steelmaking without addition of coal or carbon. The new process will directly benefit the environment since it eliminates the use of coal/coke making and therefore minimizes the release of carcinogenic gases and chemical wastes. This will lead to direct environmental and therefore social benefits for the Philippines. Furthermore, utilizing our abundant natural resources in laterite and chromite ores will improve the national economy.

Objectives:

The ultimate aim of the project is to achieve a detailed understanding of chromite and laterite ores smelting to produce Fe-Ni-Cr-C alloy and to assess the feasibility of a new, more energy-efficient technology for the direct processing of crude stainless steel.

Specific project aims are as follows:

  1. Determine the kinetics of chromite and laterite ore reduction smelting by carbon at different temperatures, ore composition and amount of fluxes.
  2. Determine the Fe, Ni, Cr and C recovery in the alloy and the slag after reduction smelting.
  3. Establish the mechanism of reduction smelting of chromite and laterite ores. Particular attention will be given to the mineralogy and phase characterisation of the ore before reduction, and changes in the ore physical state and phases in the reduction smelting process.
  4. Determine the alloy composition and lowest smelting temperature when methane pre-reduced laterite ore is mixed with raw chromite ore in the reduction smelting.
  5. Establish optimal smelting conditions for the production of Fe-Ni-Cr-C alloy from chromite and laterite ores.
  6. Assess the feasibility of the new technology for processing of chromite and laterite ores.

 

Highlights of Accomplishments

Sample preparation for smelting of 3 types of chromite ores from Zamboanga del Sur and Misamis Oriental and 5 types of laterite ores from Surigao and Palawan by calcining in a muffle furnace at 800oC for 2 hours under air to remove combined water, volatiles and decompose compounds such as carbonates. This procedure was undertaken to ensure that experimental mass loss is solely due to the reduction reaction. The lumps were crushed and sized to 100 µm.

FACTSage thermodynamic modelling was conducted to determine the effect of carbon addition and smelting temperatures on the phases formed during reduction smelting of chromite and laterite ore mixtures. A comparison of the calculated and the experimental results based on the XRD analysis will be presented. Application of the developed thermochemical databases to predict distribution equilibria between the metal and the slag in the processes of Fe-Cr-Ni-C alloy production was examined and compared with the experimental results. This would ensure an accurate result in the ongoing experiment.

Conducted non-isothermal reduction experiments of the different mixtures of laterite and chromite ores with carbon up to 1500oC. This procedure was undertaken to determine the start of reduction reaction temperatures and the kinetics of reduction.  A comparison of different reductants used in the smelting was conducted to determine the extent and rate of reduction.

 A series of experiment were carried out to determine the time required to attain the slag-metal equilibrium in terms of Ni and Cr distribution between the slag and metal. A graph of the change of Ni and Cr concentration with time in the metal and slag was presented.

Conducted reduction smelting experiments at 1600oC of five (5) types of laterite ores and three (3) types of chromite ore mixtures to determine the metal and slag formation at different carbon concentrations. Slag foaming was observed in some experiments. (Effect of carbon addition and type of ores)

Conducted preliminary reduction smelting experiments to determine the effect of flux (CaO and SiO2) addition in the smelting of mixed chromite and laterite ores. This procedure was undertaken to determine the effect of flux (CaO and SiO2) on the fluidity or viscosity of the slag. (Effect of flux addition)

 Conducted reduction smelting experiments to determine the effect of varying the temperatures in the smelting of chromite and laterite ore mixtures. This procedure was undertaken to determine the metal recovery, the kinetics, slag formation and slag viscosity. (Effect of smelting temperatures)

Conducted scanning electron microscopy (SEM) and EDS analysis on the metal and slag samples. This procedure was undertaken to determine the different phases present in the metal and the slag including the elemental analysis of each phase. Samples were also sent to UP-NIGS for XRD analysis.

Conducted wet analysis to determine the Ni, Cr and Fe concentration in the metal and the slag samples after smelting.

 Submitted a poster entitled “THERMODYNAMIC CONSIDERATIONS IN THE REDUCTION-SMELTING OF MIXED LATERITE AND CHROMITE ORES TO PRODUCE Fe-Cr-Ni-C ALLOY” for the 3rd ERDT Congress on July 30, 2014 at the SMX Convention Center, Seashell Lane, Pasay City.

Conducted thermodynamic modelling on the pre-reduction of laterite ores using methane gas as reductant. FACTSage software was used for thermodynamic optimization, heterogeneous equilibrium, and phase diagram calculations. The optimum temperature and gas concentration for the iron carbide formation was determined.

Conducted initial studies on the smelting of chromium, laterite and manganese ore mixtures to aim for AISI 204 and 214 type of steel with nominal composition of:

Type 204                  16% Cr, 2% Ni, 8% Mn, Fe bal.

Type 214                  18% Cr, 1% Ni, 15% Mn, Fe bal.

Researchers:

Dr. Nathaniel M. Anacleto

Dr. Nathaniel M. Anacleto

Ph.D. in Metallurgical Engineering, University of New South Wales, Australia

Project Leader

MSU-Iligan Institute of Technology

Engr. Nadzmi S. Sayadi

Engr. Nadzmi S. Sayadi

Project Staff

Master of Teaching Technology (Met.E.)

MSU-Iligan Institute of Technology 

Engr. Jessa Leigh Mordeno

Engr. Jessa Leigh V. Mordeno

Research Assistant

 BS Chemical Engineering

MSU-Iligan Institute of Technology