Indirect mineral carbonation of blast furnace slag with(NH4)2SO4 as a recyclable extractant

Journal of Energy Chemistry26(2017)

927–935

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journal-of-energy-chemistry/

Contents l i sts a v ai l a ble a t Sc i enceD i rect

Journal of Energy Chemistry

j ourn a l ho m ep a ge:www.elsev i er.co m/loc a te/j eche m

Indirect mineral carbonation of blast furnace slag with(NH4)2SO4as a recyclable extractant

Jinpeng Hu,Weizao Liu,Lin Wang,Qiang Liu,Fang Chen,Hairong Yue,Bin Liang,Li Lü,

Ye Wang,Guoquan Zhang,Chun Li∗

College of Chemical Engineering,Sichuan University,Chengdu610065,Sichuan,China

a r t i c l e i n f o

Article history:

Received11April2017

Revised17June2017

Accepted19June2017 Available online30June2017

Keywords:

Blast furnace slag

CO2

Mineral carbonation

CO2sequestration a b s t r a c t

Large quantities of CO2and blast furnace slag are discharged in the iron and steel industry.Mineral car-bonation of blast furnace slag can offer substantial CO2emission reduction and comprehensive utilisation of the solid waste.In this study,a recyclable extractant,(NH4)2SO4,was used to extract calcium and magnesium from blast furnace slag(main phases of gehlenite and akermanite)by using low-temperature roasting tofix CO2through aqueous carbonation.The process parameters and efficiency of the roasting extraction,mineralisation,and Al recovery were investigated in detail.The results showed that the ex-tractions of Ca,Mg,and Al can reach almost100%at an(NH4)2SO4-to-slag mass ratio of3:1and at370°C in1h.Adjusting the pH value of the leaching solution of the roasted slag to5.5with the NH3released during the roasting resulted in99%Al precipitation,while co-precipitation of Mg was lower than2%.The Mg-rich leachate after the depletion of Al and the leaching residue(main phases of CaSO4and SiO2)were carbonated using(NH4)2CO3and NH4HCO3solutions,respectively,under mild conditions.Approximately 99%of Ca and89%of Mg in the blast furnace slag were converted into CaCO3and(NH4)2Mg(CO3)2•4H2O, respectively.The latter can be selectively decomposed to magnesium carbonate at100–200°C to recover the NH3for reuse.In the present route,the total CO2sequestration capacity per tonne of blast furnace slag reached up to316kg,and313kg of Al-rich precipitate,1000kg of carbonated product containing CaCO3and SiO2,and304kg of carbonated product containing calcium carbonate and magnesium car-bonate were recovered simultaneously.These products can be used,respectively,as raw materials for the production of electrolytic aluminium,cement,and light magnesium carbonate to replace natural re-sources.

©2017Science Press and Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published

by Elsevier B.V.and Science Press.All rights reserved.

1.Introduction

Carbon dioxide capture(utilisation)and storage(CCS/CCUS)is recognised as one of the options for tackling the increase in the at-mospheric concentration of CO2for climate change mitigation[1]. Although a huge amount of CO2can be stored through geologi-cal and oceanic sequestration,proper geological conditions,such as depleted oil and gasfields,and geographical conditions,e.g.close to deep sea for the CO2sources,as well as the inevitable use of expensive monitoring equipment to ensure that CO2does not es-cape into the atmosphere for a very long time are required.Min-eral carbonation is a potential CO2sequestration method in which calcium and magnesium oxides in various minerals,particularly sil-

∗Corresponding author.

E-mail address:lic@(C.Li).icate minerals,react with CO2and form thermodynamically stable carbonates.Silicate rocks are abundant in nature to the extent that, in theory,the potential for CO2storage by mineral carbonation is higher than those of other CO2storage methods[2].

Mineral carbonation consists of direct and indirect methods. The former mimics the weathering process in nature but proceeds at a much faster rate which can be enhanced using a variety of methods,including activation pre-treatment of minerals[3],the use of a high temperature and pressure[4,5],and high-gravity methods[6].However,the products of direct mineral carbonation are generally mixtures,which are difficult to separate for further utilisation or for selling as valuable products.Indirect CO2miner-alisation ordinarily comprises two successive steps:(1)extraction of Ca and Mg from minerals with an acidic or weakly acidic ad-ditive and(2)carbonation of Ca-and Mg-rich solutions or solids with CO2in a basic or weakly basic environment.This method is now receiving widespread attention because of its relatively mild

/10.1016/j.jechem.2017.06.009

2095-4956/©2017Science Press and Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.and Science Press.All rights reserved.