Calcination-free production of calcium hydroxide at sub-boiling temperatures. Issue 3 (6th January 2021)

• Record Type: Journal Article
• Authors: Vallejo Castaño, Sara; Callagon La Plante, Erika; Shimoda, Sho; Wang, Bu; Neithalath, Narayanan; Sant, Gaurav; Pilon, Laurent
• Is Part Of: RSC advances. Volume 11:Issue 3(2021)
• Page Start: 1762
• Page End: 1772
• Publication Date: 2021-01-06
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra08449b
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : A calcination-free route to produce calcium hydroxide from alkaline industrial wastes including leaching, concentration, and temperature-swing precipitation. Abstract : Calcium hydroxide (Ca(OH)2 ), a commodity chemical, finds use in diverse industries ranging from food, to environmental remediation and construction. However, the current thermal process of Ca(OH)2 production via limestone calcination is energy- and CO2 -intensive. Herein, we demonstrate a novel aqueous-phase calcination-free process to precipitate Ca(OH)2 from saturated solutions at sub-boiling temperatures in three steps. First, calcium was extracted from an archetypal alkaline industrial waste, a steel slag, to produce an alkaline leachate. Second, the leachate was concentrated using reverse osmosis (RO) processing. This elevated the Ca-abundance in the leachate to a level approaching Ca(OH)2 saturation at ambient temperature. Thereafter, Ca(OH)2 was precipitated from the concentrated leachate by forcing a temperature excursion in excess of 65 °C while exploiting the retrograde solubility of Ca(OH)2 . This nature of temperature swing can be forced using low-grade waste heat (≤100 °C) as is often available at power generation, and industrial facilities, or using solar thermal heat. Based on a detailed accounting of the mass and energy balances, this new process offers at least ≈65% lower CO2 emissions than incumbent methods of Ca(OH)2, and potentially, cement production.