Investigation of Mineral Carbonation with Direct Bubbling into Concrete Sludge

Abstract

Mineral carbonation, which is CO 2 fixation through a carbonation reaction using alkaline earth metals, is being investigated as a carbon capture and utilization method to reduce CO 2 atmospheric emissions. Concrete sludge is an alkali waste material from the concrete industry and contains abundant calcium components. We investigated the applicability of concrete sludge for mineral carbonation. In this study, gas containing CO 2 was bubbled through the model concrete sludge solution and the effects of the solid−liquid ratio, bubbling time, gas flow rate, and the partial pressure of CO 2 on the CO 2 fixation ratio and fixation rate were investigated. The CO 2 fixation ratio decreased with increasing CO 2 bubbling time, CO 2 flow rate, and CO 2 partial pressure. The CO 2 fixation rate increased with increasing CO 2 flow rate and CO 2 partial pressure. The formation of calcite, a form of calcium carbonate, was confirmed.

Preparation of High-Purity Calcium Carbonate by Mineral Carbonation Using Concrete Sludge

“…The equilibrium concentration of calcium ions and pH under pCO 2 = 0.1 atm are, respectively, 129 mg/L and 6.61, based on the thermodynamic analysis, which are shown by the dotted line and the dashed line in Figure 5 . 25 The observed calcium concentration decreased below the equilibrium concentration after 12 min, reached the minimum value at 22 min, and gradually approached the equilibrium value. The observed pH monotonously approached the equilibrium value, which the observed pH reached after 60 min.…”

“…The mixture was placed in a plastic bottle and stirred for 24 h on a roller mixer (40 rpm) to be fully hydrated. 25 The elemental composition of Portland cement is 46.4% Ca, 10.2% Si, 1.1% Fe, and 1.4% Al. The model concrete sludge after hydration for 24 h was filtered through a cellulose filter with a pore diameter of 20–25 μm.…”

“… 15 , 20 On the other hand, fresh concrete waste or concrete sludge is under-hydrated and highly reactive with CO 2 , and it can be carbonated by direct contact with CO 2 gas even under ambient conditions. 10 , 17 , 24 In our previous study, 25 we reported a carbonation process of model concrete sludge with direct bubbling of CO 2 -containing gas into model concrete sludge. The carbonation reaction of model concrete sludge was found to proceed quickly, and dissolved calcium ions from hydrated cement (as calcium hydroxide) can be almost completely transformed and precipitated as calcium carbonate.…”

“…The results of the carbonation performances were compared with those for the conventional method of carbonation of concrete sludge by the direct carbonation method. 25 …”

CO2 mineralization of demolished concrete wastes into a supplementary cementitious material – a new CCU approach for the cement industry

“…However addition of RCP results in an increased water demand for the composite cements [19]. The enforced carbonation techniques were explored to modify the properties of the RCP, initially by Iizuka et al [20][21][22][23][24] and Ghacham et al [25,26]. Fang et al [27,28] have investigated a two-step wet-carbonation process which allows valorization of recycled cement paste into the added value products of calcite and alumina-silica gel.…”