Elsevier

Hydrometallurgy

Volume 203, August 2021, 105622
Hydrometallurgy

Production of ferronickel from limonitic laterite ore using hydrogen reduction and cementation

https://doi.org/10.1016/j.hydromet.2021.105622Get rights and content

Highlights

  • A hydrometallurgical process to recover Ni from limonitic laterite was introduced using hydrogen reduction and cementation.

  • The introduction of the reusability of H2-reduced limonitic laterite as a cementation agent is an important approach.

  • The Ni was recovered as ferronickel cement to apply in steel smelter as an intermediate.

  • Ni cementation behavior can be elucidated by applying 1st order reaction kinetics.

  • The activation energy of the Ni cementation was deduced as 7.5 kJ/mol.

Abstract

Production of ferronickel from limonitic laterite ore using hydrogen reduction and cementation was studied by relying on a novel hydrometallurgical process consisting of the key steps: calcination, reductive roasting with hydrogen gas, 2-stage atmospheric hydrochloric acid leaching, and cementation with Fe. The introduction of the reusability of H2-reduced limonitic laterite as a cementation agent instead of conventional Fe sources is an important approach of the proposed process in terms of enhancing cost-effectiveness. The effects of the type of Fe source, the amount of cementation agent, and the temperature on Ni cementation were experimentally determined. The kinetic analysis confirms that Ni cementation behavior can be elucidated by applying 1st order reaction kinetic principles, and the temperature is the most effective parameter. Based on the linear relationship of empirical data with the 1st order kinetic model and by the calculations associated with Arrhenius law, the value of the activation energy of Ni cementation onto Fe could be deduced as 7.5 kJ/mol. Greater than 99% of Ni could be recovered under the most suitable conditions, and the final product was obtained as ferronickel cement (Ni 10%), which can be applied in steel smelter as a prominent intermediate.

Introduction

Nickel is one of the most strategic metals, which has a wide range of applications. According to its purity, applications of Ni can be classified as class-1 Ni and class-2 Ni. The main applications of class-1 Ni include cathode, pellets, powder and batteries. The ferronickel, intermediate to steel-making, and nickel salts in the chemical industry are categorized as typical applications of class-2 Ni. Despite the fact that Ni appears in about 20 different mineral varieties, only sulfide ore and laterite ore are valuable natural sources where Ni can be extracted economically. Sulfide ores are found on the surface of the earth's crust and also thousands of meters underground. Laterite ores are formed by exposure of Ni-containing rocks to the atmosphere for a long time. Furthermore, the average Ni contents in sulfide and laterite ores are 0.68% and 1.28%, respectively. However, the ratio of sulfide ore to laterite ore found in most sources is about 28:72 (McDonald and Whittington, 2008), and the ratio of Ni production from them is 58:42, respectively. The major Ni-bearing sulfide mines are limited to Canada, Russia, Australia, and South Africa, while most of the laterite mines exist in Cuba, New Caledonia, Indonesia, Philippines, and Australia.

Laterite ore is a well-known raw material, where Ni and Fe exist as oxides. It can be diversified into limonite, saprolite, and garnierite, particularly with respect to the depth from the earth's surface, the characteristics, and average chemical composition, as exhibited in Table 1(N.W. Brand et al., 1998). Limonitic laterite exists near to earth surface with low Ni content (0.8–1.5%), while saprolite laterite having higher Ni content (1.8–3.5%) is deposited at a higher depth. In fact, there are two main types of limonitic laterite ores recognized as red and yellow limonite. The Fe content of red limonite is higher than yellow limonite, where Ni content is extensively low. Hydrometallurgical processes, pyrometallurgical processes, and hydro-pyro hybrid processes are prevalent Ni extracting technologies implemented in processing laterite ores. The pyrometallurgical processes are mostly employed to produce ferronickel from laterite ore by relying on different techniques such as drying, calcination, reduction, and smelting using electric furnaces. However, the main drawbacks of these types of techniques are massive energy consumption and Ni loss in slag. Consequently, laterite smelters tend to be established only in areas with low electricity costs and process only high Ni-bearing laterite ores. Moreover, the pyro-hydro hybrid processes employ the Caron process, and the hydrometallurgical processes use the high-pressure acid leaching (HPAL) technique (Whittington, 2000). However, the Caron process is no longer commercially viable due to the low recovery of Ni, the high installation, and operational cost. The HPAL process also has no sufficient demand from the industry due to scale formation during the autoclave operation, high capital expenditure, and extensive acid and energy consumption in recent times.

Considering the aforementioned drawbacks of Ni extracting technologies, a novel hydrometallurgical process was introduced in this study, which brings benefits of low energy consumption, low maintenance cost, and high recovery of Ni. The proposed process is economically feasible to process limonitic laterite ore with low Ni content and high Fe content on a commercial scale with the goal of producing law-grade ferronickel cement as the final product. This process consists of the key steps: calcination, reductive roasting with hydrogen, 2-step atmospheric leaching, and cementation. The flow diagram of this novel process with targeted impurity removal at each step is illustrated in Fig. 1. The leading reactions taking place at each stage are given in Eqs. (1), (2), (3), (4). However, in this paper, the main focus is the hydrogen reduction and cementation steps. In particular, the cementation behavior of Ni onto Fe from hydrochloric acid leaching solution of H2-reduced limonitic laterite and its kinetic analysis with the aid of empirical data and theoretical calculations were investigated in detail.

The effect of the type of cementation agent to cement nickel from the filtrate of 2nd hydrochloric acid leaching of H2-reduced limonitic laterite was investigated using Fe scrap, Fe powder, H2-reduced limonitic laterite as cementation agents. As the primary target of this work is producing low-grade ferronickel cement as an intermediate to the steel-making industry, Fe was selected as the reductant instead of other more active reductants, such as Zn and Al with the goal of avoiding contamination of the final product from the remaining cementation agent. In particular, the idea of introducing H2-reduced limonitic laterite ore as a cementation agent was a remarkable approach in terms of industrial practicability. The reductive roasting of limonitic laterite with hydrogen gas was introduced as an amenable pretreatment for the leaching process (Hadi Purwanto et al., 2003) and for preparing cementation agent. Utilizing hydrogen gas as a reductant instead of inexpensive carbon monoxide may be a controversial point of this work. Several studies have been carried out to compare the reduction of the nickeliferous limonitic laterite ore with hydrogen versus carbon monoxide and highlighted the unique benefits of hydrogen reduction. The reduction of laterite ore using hydrogen could occur at lower temperatures so that the temperature required for maximum recovery of target metal is lower for hydrogen than for carbon monoxide. Furthermore, previous studies (Elliott and Pickles, 2016) revealed that the required temperature range for high Ni recovery was much wider for hydrogen than for carbon monoxide. In carbon monoxide, the iron recovery followed the nickel recovery, while in hydrogen, the amount of iron continuously increased with temperature, and consequently, the quality of the ferronickel was lower at higher production temperatures. In general, hydrogen reduction is associated with producing lower-grade ferronickel and higher recoveries compared to reduction with carbon monoxide. Also, there has been growing interest in responsible investment (RI) and responsible sourcing (RS) from the perspective of ESG (Environmental Social Governance) concept in recent years. In particular, techniques of the utilization of eco-friendly hydrogen gas instead of carbon monoxide have gained appreciable demand in terms of reducing global CO2 emission from industries. Moreover, the environmental regulations have been updated in South Korea, which introduces a penalty payment system for using carbon sources as reductants with the goal of diminishing CO2 emission. The capability of reusing hydrogen gas generated from the leaching and cementation stages of the proposed process (Fig. 1) is a notable cost-effective benefit in this study.Reductive roasting:MxOys+H2gMs+H2Ol,whereM=Fe,Ni,Co1st Stage leaching:Fes+2HClaqFeCl2aq+H2g2nd Stage leaching:Nis+2HClaqNiCl2aq+H2gCementation:Ni2+aq+FesFe2+aq+Nis

Section snippets

Hydrogen reduction

The fin-tube furnace (Model SFTS-60) was employed for hydrogen reduction of limonitic laterite on a laboratory scale, as illustrated in Fig. 2 (a). As shown in the schematic diagram of the hydrogen reduction step, hydrogen gas was purged into the horizontal tube after mixing with argon gas in order to vary the hydrogen concentration. The limonitic laterite ore sample was placed in the alumina boat and allowed to contact hydrogen gas at the desired temperature for a pre-calculated time period.

Characterization of cementing materials and leach liquors

The initial solution for cementation tests was prepared by leaching H2-reduced limonitic laterite (Ni 2.2%, Fe 67.3%) collected from New Caledonia with the aid of the proposed process under the most suitable conditions as mentioned above. The chemical composition of the initial solution used for cementation tests is given in Table 4, which contains Ni (6000 mg/L) and Fe (8000 mg/L) as major constituents.

The XRD analyses of limonitic laterite ore used in this work before and after hydrogen

Conclusion

The cementation behavior of Ni onto Fe in H2-reduced limonitic laterite ore was investigated using the proposed novel hydrometallurgical process for valorizing low-grade Ni ore. The proposed process with a complete analysis of initial raw material, H2-reduced ore, 2nd leach residue, and ferronickel product is illustrated in Fig. 14, including the approximate compositions. Indeed, the capability of utilizing H2-reduced limonitic laterite ore as a cementation agent instead of conventional Fe

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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