Insights Into Nickel Slag Carbonation in a Stirred Bead Mill

Carine Julcour,Imane Benhamed,Jaouher Diouani,Laurent Cassayre,Florent Bourgeois

doi:10.3389/fceng.2020.588579

Abstract

This work is part of the ongoing development of the attrition-leaching carbonation process, a single-step aqueous carbonation technology that integrates a stirred bead mill. The principle of the attrition-leaching carbonation process is to continuously refresh the surfaces of reactive particles so that leaching can proceed unimpeded, yielding enhanced carbonation kinetics and yield. Invariably, attrition-leaching carbonation experiments carried out under controlled temperature and CO2 partial pressure conditions with different silicate-rich carbonation feedstocks - natural ores and nickel slags - show a carbonation yield that tends towards a plateau 20 to 50% below the stoichiometric yield. This repeatable behaviour raises the question as to whether the carbonation limitation is due to specific equilibrium side reactions of the carbonation feedstock or to a kinetic limitation of the attrition-leaching carbonation process. To try to provide some answers to this puzzling question, this reflexive paper implements a “thermo-kinetic” modelling methodology based upon geochemical equilibrium simulations and particle reaction models. The results obtained indicate that the observed slowing down of the carbonation process can be explained either by the formation of Mg- and/or Fe-rich silicates that precipitate at the expense of carbonates, or by a decrease in the efficiency of the attrition process over time. Indeed, either one of these mechanisms could explain the observed behaviour of the attrition-leaching carbonation process. However, the cross comparison of different data sources pleads in favour of the attrition-leaching carbonation performance being limited by the attrition process. Pending further confirmation, this tentative conclusion suggests that further development of the attrition-leaching carbonation process requires new knowledge about its inner workings, and that there may be ways to optimize the performance of this process beyond that based on standard stirred bead mill operating rules.

Highlights

For several years aqueous mineral carbonation has stood out as a viable solution for CO2 sequestration in the form of stable carbonates, and as a way of treating or recovering littleexploited minerals or mining industry wastes (Huijgen et al, 2005; Sipilä et al, 2008; Bodor et al, 2013; Sanna and Maroto-Valer, 2017; Veetil and Hitch, 2020)
Thermodynamic simulations performed at 175°C predicted that the iron extracted from the steel beads could be converted to either minnesotaite or siderite and Fe-Mg saponite, depending on the system considered (Figure 9). These results prove that an accurate thermodynamic description of the various phyllosilicates formed is of primary importance to evaluate the contribution of iron pollution to the carbonation yield
Owing to the continuous renewal of reactive surfaces that goes beyond a simple particle size reduction effect, the attritionleaching carbonation process has been shown to strongly improve the carbonation yield of natural minerals and industrial residues alike

Summary

Introduction

Aqueous mineral carbonation has stood out as a viable solution for CO2 sequestration in the form of stable carbonates, and as a way of treating or recovering littleexploited minerals or mining industry wastes (Huijgen et al, 2005; Sipilä et al, 2008; Bodor et al, 2013; Sanna and Maroto-Valer, 2017; Veetil and Hitch, 2020). The attrition-leaching carbonation process (Julcour et al, 2015; Bourgeois et al, 2020) has made it possible to remove all or part of these diffusion barriers, enabling the conversion of more than 50% of carbonatable species in about 10 h This process uses the direct aqueous carbonation route, whose chemistry relies on two main features: 1) gaseous CO2 is the only reactant; 2) CO2 hydrolysis provides the proton source for the dissolution of the solid phase in water (see Figure 1). This is a complex system with several concomitant mechanisms (see Figure 1): attrition, but probably particle breakage, chemical attack of the reactive feedstock phases, gas dissolution and precipitation of product phases

Methods

Results

Conclusion