Enhanced extraction of nickel from limonitic laterite via improved nitric acid pressure leaching process
Introduction
Nickel is a hard, ductile and ferromagnetic metal that is utilized in a variety of applications including stainless steel, alloy steel, batteries, and electroplating (Ilyas et al., 2020, Lei et al., 2020, Ma et al., 2020). As economically available nickel sulfide resources become increasingly depleted, laterite, which is low grade and technically difficult to treat, is gaining popularity (Forster et al., 2016, Wang et al., 2019, Zhu et al., 2012). There are two types of lateritic nickel oxide ores - silica-magnesium based saprolitic ore and goethite based limonitic ore with nickel grade of 1.8%–4.0% and 0.8%–1.8%, respectively (Asadrokht and Zakeri, 2022, Georgiou and Papangelakis, 2009, He et al., 2022a). The laterite is by far the most widely available nickel oxide ore, containing nickel, iron, magnesium, cobalt, manganese, aluminium and scandium, and has the advantage of being easy to explore, less difficult to mine and less costly. However, the laterite ores are complex in composition, fluctuate greatly in composition and contain low nickel grades, so the research on nickel extraction from laterite ores has been of considerable interest (Putzolu et al., 2020, Tupaz et al., 2020, Ugwu et al., 2019).
There are two main treatment processes for nickel laterite ores: pyro-metallurgical process and hydro-metallurgical process (Li et al., 2013, Ma et al., 2015). The relatively mature treatment processes are rotary kiln calcination-electric furnace smelting; (RKEF), Caron reduction roast-ammonia leaching, and high pressure acid leach (Sarbishei and Tafaghodi, 2020, Senanayake et al., 2011, Stanković et al., 2020, Whittington and Muir, 2000). For limonitic laterite ores, our group has proposed a nitric acid pressure leaching process (Ma et al., 2015, Ma et al., 2013). In comparison to the sulphuric acid pressure leaching process, the process has the advantage of mild reaction conditions and high extraction of nickel and cobalt at lower temperatures and pressures. The reagent consumption is low, and the leaching reagent and neutralizing reagent can be regenerated, while the residue is suitable for the complete use of iron and chromium as it does not contain sulphur (The residue is used as a raw material for blast furnace ironmaking.).
Therefore, a systematic study of each technical aspect of the process has been carried out. In our previous work, the porous kinetics of nitric acid pressure leaching of limonitic laterite was investigated. The results show that the leaching of nickel is consistent with grain model-pore diffusion control (He et al., 2022a, He et al., 2022b, He et al., 2023). In response to this conclusion, two options for enhanced laterite leaching are proposed. The improved process flow diagram is shown in Fig. 1. The first option is to enhance the leaching by bleeding air from the slurry. Due to the high porosity of limonitic laterite (62.06%), when it is submerged in solution, gases are inevitably carried within the pores. The residual gas inside the laterite can be removed by negative external pressure. In this way, the interfacial chemical reaction area can be increased and the dissolution of the laterite ore accelerated. The second option is to enhance the leaching by adding surfactants to the slurry. Surfactants can reduce the surface tension of the solution and change the wettability of the mineral surface in the leaching system, so that the ore and the solution have a larger contact area, especially to facilitate the solution into the pores and fissures of the ore, accelerating the dissolution of minerals (Ai et al., 2019, Chen et al., 2022, Ding and Ren, 2020, Tapera et al., 2018). In addition, the addition of surfactants reduces the thickness of the liquid film on the ore surface, accelerating convective diffusion and mass transfer (Behari et al., 2022, Liu et al., 2019, Pan et al., 2020). George Owusu investigated the effect of surfactants on the leaching of sphalerite. The results showed that when surfactants were present, the extraction of zinc was over 99% (Orthophenylene diamine), 86–94% (Lignin sulfonic acid) and 96–98% (metaphenylene diamine) respectively. In contrast, in the absence of surfactant, the zinc extraction was only 50% (Owusu, et al., 1995). Zhang used surfactants to enhance the extraction of nickel from serpentine laterite. The results showed that the surfactant enhanced the atmospheric leaching of the laterite ore and improved the nickel and cobalt recovery (Zhang et al., 2021, Zhang et al., 2019).
Based on the study of the porous kinetics of nitric acid pressure leaching of limonitic laterite, this paper firstly analyses the effects of time, temperature, liquid/solid and nitric acid concentration on Ni and Fe extraction using the response surface methodology. Response surfaces and equations are obtained. Enhancement experiments were then carried out using the optimum process parameters recommended by the response surface methodology. Both bleed air and surfactants were considered for the Enhancement experiments. Ultimately, the enhancement mechanisms of bleeding air and adding surfactants on leaching limonitic laterite were summarized by studying the leaching behaviour of nickel and iron.
Section snippets
Materials
The laterite utilized in the experiment is a reddish brown, clay-like material from Indonesia. The laterite contains 47.91% iron and 1.12% nickel. The size of the raw material is small, with an average particle size of 4.99 μm and a porosity of 62.06% (Supplementary file Note 1). It is a typical limonitic laterite. The phase and micromorphology of the laterite are shown in Fig. 2. It indicates that the main phases are goethite and a type of spinel. Goethite appears as elongated rod-like
Optimizing the process conditions via response surface methodology
The response surface methodology is a test statistics method for improving stochastic processes, often known as a regression design, with the goal of identifying quantitative patterns between test indicators and factors and determining the best combination of factor values (Pattanaik and Rayasam, 2018, Polat and Sayan, 2019, Qiu et al., 2018).
The experiments investigated the effects of time, temperature, liquid to solid and nitric acid concentration on the Ni and Fe extraction. The experimental
Conclusion
In this paper, response surface methodology was first used to optimize the parameters of the nitric acid pressure leaching process for limonitic laterite ores, and then the optimized process conditions were used to carry out enhanced leaching experiments and to analyses the enhancement mechanism. The conclusions are as follows:
Based on the results of the batch tests, the effects of time, temperature, liquid/solid, and nitric acid concentration on the Ni and Fe extraction were simulated using
CRediT authorship contribution statement
Fei He: Conceptualization, Writing – original draft, Writing – review & editing. Baozhong Ma: Writing – review & editing, Supervision, Funding acquisition. Zhijun Qiu: Review & Editing. Chengyan Wang: Supervision, Project administration. Yongqiang Chen: Supervision, Visualization. Xiujuan Hu: Review.
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.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (U2202254, 51974025), and the Fundamental Research Funds for the Central Universities (FRF-TT-19-001).
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