Abstract
In this study, the possibility of using concrete-sludge recycling as an immobilizer, including dried sludge (DS), precipitated calcium carbonate (PCC), and calcite-coated particles (CCP), was evaluated for the remediation of Cu-, Pb-, and Zn-contaminated aqueous solutions. Experimental variables characterizing immobilization, including reaction time, initial solution pH, and immobilizer dosage, were selected. After DS was applied, 98.3% of Cu, 99.9% of Pb, and 95.2% of Zn were removed via metal-hydroxide coprecipitation onto the surface of DS, which increased in pH within the shortened contact time. On the contrary, PCC and CCP removed metals (above 99.9% removal) via the formation of metal carbonates, which was highly dependent on both the pH and the carbonates released from the immobilizers. The acidic solution pH contributed to the dissolution of calcite (leading to an increase in carbonates in solution), thus enhancing the removal of metals. An increase in PCC and CCP dosage (liquid to solid ratio of 1000 to 100) was effective in removing Cu with an increasing final pH and number of carbonates in solution. Our results show that concrete sludge can be recycled to reduce environmental loads, including alkaline wastewater discharge, waste disposal, CO2 emissions, and metal-contaminated aqueous solutions.
Highlights
The metallic contamination of groundwater by industrial developments and human activities have serious, harmful effects on human health and the ecosystem
The main purpose of this study was to evaluate the applicability of immobilizers derived from concrete sludge for the removal of Cu, Pb, and Zn from aqueous solution
Dried sludge (DS) and calcite-predominant particles were produced via a wet-sieving method using a 25 μm sieve and a carbon mineralization process, respectively
Summary
The metallic contamination of groundwater by industrial developments and human activities (e.g., mining, smelting, and refining) have serious, harmful effects on human health and the ecosystem. The immobilization method using Fe/Mn/Al oxides, clay minerals, or calcium (Ca)-bearing amendments is an attractive technique for the inhibition of the mobility and toxicity of metallic contaminants in a groundwater environment [3,4]. Ca-bearing materials/waste/minerals, such as gypsum (CaSO4 ·2H2 O), quicklime (CaO), slaked lime (Ca(OH)2 ), fly ashes, hydroxyapatites (Ca5 (PO4 ) (OH)), and limestone (CaCO3 ), are attractive alternative immobilizers that are accessible and cost-effective for reducing contamination [5,6,7,8,9,10]. Screening and crushing processes are essential for the recycling of waste concrete as aggregate materials, which are classified as dry- and wet-based processes
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