Abstract
In this work, the precipitation of high-quality calcium carbonate (PCC) from synthetic Ca-rich solutions was investigated. A mixture of Ca and Mg salts were considered to reproduce the chemical composition of leachates obtained from leaching BOF slags with diluted HCl. The effect of adding NaOH and different amine-based organic solvents (PEI, MEA and AEEA) was investigated by considering an integrated process: CO2-absorption and mineral carbonation. Ca conversion was below 15 wt.% in the absence of alkaline reagents as alkalinity is reduced when H2CO3 is formed under permanent introduction of CO2. The addition of a substantial amount of NaOH (20 g/L, Ca/Na ratio of 1:1) allowed to significantly increase the Ca-conversion yield, and the morphology of calcite particles was modified from scalenohedral-rhombohedral-type to rhombohedral shape by increasing the CO2-gas flow rate from 0.008 to 0.5 L/min. During carbonation with the addition of amine-based organic solvents, MEA and AEEA showed the highest Ca-conversion, i.e. > 80 wt.%. A combination of vaterite and aragonite particles were produced at 30 °C, while the formation of pure aragonite prevailed when the temperature was increased up to 70 °C. The effect of Mg on the formation of aragonite particles was considered negligible due to the low initial concentration, although some traces of Mg were detected in the corresponding final PCC particles.
Highlights
Steelmaking is an energy-intensive process that consumes ca. 19 GJ (considered in the Blast Furnace (BF) – Basic Oxygen Furnace (BOF) processes) and emits ca. 1.9 tonne of CO2 per tonne of crude steel [7,8]
Ca conversion was below 15 wt.% in the absence of alkaline reagents as alkalinity is reduced when H2CO3 is formed under permanent introduction of CO2
A combination of vaterite and aragonite particles were produced at 30 oC, while the formation of pure aragonite prevailed when the temperature was increased up to 70 oC
Summary
Steelmaking is an energy-intensive process that consumes ca. 19 GJ (considered in the Blast Furnace (BF) – Basic Oxygen Furnace (BOF) processes) and emits ca. 1.9 tonne of CO2 per tonne of crude steel [7,8]. Ammonium salt solutions have demonstrated a good performance to extract Ca from steel converter slags and subsequently produce precipitated calcium carbonate (PCC), with a Ca extraction efficiency that varies between 40-60 wt.%, depending on the availability of free lime (CaO) in the slag [21,23,24,25]. Other mineral acids, such as acetic acid (CH3COOH), sulfuric acid (H2SO4), nitric acid (HNO3) and hydrochloric acid (HCl), to extract Ca and/or Mg from silicate minerals have been reported [26,27,28,29,30]. The precipitation of the extracted Ca (and Mg) can be performed with the aid of NaOH [30,31]
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