Low-grade magnesium oxide by-products for environmental solutions: Characterization and geochemical performance

Abstract

The reutilization of the by-products from the calcination of natural magnesite for environmental solutions is conditioned by the availability of MgO, CaO and other compounds. In order to overcome their great heterogeneity, an exhaustive chemical and physical characterization is necessary in order to assess their potential applications. In this study, the acid neutralization capacity (ANC) test was used to categorize three types of byproducts (LG-MgO, LG-D and LG-F), which mainly differed according to source ore and processing conditions. The experimental data concerning the leaching of Mg 2+ , Ca 2+ , Fe 2+ and SO 4 2− was corroborated with geochemical predictions using the modelling software Visual MINTEQ. Likewise, the main solubility-controlling mineral phases were also identified. According to the results, there is a buffer capacity within the pH 8-10 range, mainly dominated by the neutralization of MgO/Mg(OH) 2 , equilibrium with a small contribution from the carbonate content at lower pH values. The release of sulphates showed a non-pH dependency attributed to the solubility of CaSO 4 and elemental sulphur present in petcoke. For dust materials, leaching of Fe was minimal above pH 6 owing to the insoluble nature of the Fe 2 O 3 /Fe 3 O 4 pair. Accordingly, the by-products labeled as LG-D and LG-F are better suited for stabilizing solid wastes or wastewater that are acid while LG-MgO is more appropriate for alkaline residues such as contaminated soils. In both cases, a suitable pH range in which pH-dependent heavy metals and metalloids show minimum solubility can be obtained. The use of these by-products guarantees an environmentally friendly alkali reservoir for the long-term stabilization of heavy metals and metalloids at a very competitive price as a substitute for the widely used lime.

Transposition of wet flue gas desulfurization using MgO by-products: From laboratory discontinuous batch reactor to pilot scrubber

“…Therefore, pH S was well predicted by laboratory experiments. This three-step neutralization behaviour is related to the alkaline phases contained in the by-product and it was early described by the authors at laboratory scale by means of geochemical modelling and the acid neutralization capacity (ANC) [3]. Thus, the lineal section is attributed to the equilibrium solubility of the pair Mg(OH) 2 /MgO.…”

“…As it can be seen, it is formed by several alkaline phases (carbonates, oxides and hydroxides) that are mainly magnesium-based (MgO~50 wt.% and MgCO 3~2 0 wt.%), although it presents a significant amount of limestone (~17 wt.%). The acid neutralization capacity of these phases has been described elsewhere [3]. At pH N 9.5 the equilibrium solubility of the pair MgO/Mg(OH) 2 is the controlling phase under acidic conditions while the buffering capacity in the 8-4 pH range can be described by the equilibrium of HCO 3 − /CO 3 2 − [17,18].…”

“…2 shows the pH profile recorded as a function of experimental time during both tests. As it can be seen, the decrease of pH as desulfurization took place proceeded in three-stages [3]. An initial stage controlled by the solubility of the alkaline oxides was characterised by a sharp reduction from the natural pH of the by-product (~10.5-11) to the 7-8 range.…”

“…In this aspect, the authors already reported the reutilization of several by-products from the obtaining of magnesium oxide with a 100% removal efficiency using a discontinuous batch reactor [2]. These by-products are obtained from the calcination process of natural magnesite and are characterised for being a mixture of mainly magnesium (hydr)oxides and different proportions of calcium (hydr)oxides, dolomite, siliceous materials and other minor inorganic compounds [3]. For this reason, their performance is controlled by several alkaline phases with different buffering capacities that slightly differed from the widely used lime-based absorbents.…”

Comparison of mechanical and leaching behaviours of pulverised fuel ash/low-grade magnesium oxide-cement blended stabilised/solidified baghouse dust

“…The right choice and effective use of binders in S/S is important since they physically and chemically trap contaminants. Portland cement and lime have been widely used as primary binders while ground granulated blast furnace slag (GGBS), pulverised fuel ash (PFA), natural pozzolans, low grade magnesium oxide and silica fume are widely used as secondary binders (Alsheyab & Khedaywi, 2013;Arribas, Santamaría, Ruiz, Ortega-López, & Manso, 2015;Chang, Lin, Ko, & Liaw,1999;Chen, Tyrer, Hills, Yang, & Carey, 2009;del Valle-Zermeño, Giro-Paloma, Formosa, & Chimenos, 2015;Fernandez, Macias, Guerreo, Lorenzo, & Goni, 2000;Gervais & Ouki, 2000, 2002, Lampris, Stegemann, & Cheeseman, 2008, 2009a, 2009bParia & Yuet, 2006;Pasetto & Baldo, 2010;Poon, Lio, & Tang, 2001; Rodrfguez-Piñero, Pereira, de Elvira Francoy, & Vale Parapar, 1998;Salihoglu & Pinarli, 2008;Serjun et al, 2015;Shi & Spence, 2004;Stegemann & Zhou, 2009).…”