Search Results (4)

Utilizing a variety of solid wastes to prepare alkali-activated cementitious materials is one of the principal trends in the development of cementitious materials. Commonly used alkali activation precursors such as granulated blast furnace slag (GBFS) and fly ash (FA) will be less available due to resource pressures. Supply limitation is an important reason to research alternative precursors. To realize the high value-added utilization of copper–molybdenum tailings (CMTs), this study adopted the modified sodium silicate solution as an alkaline activator to activate GBFS-FA-CMTs cementitious system to prepare alkali-activated cementitious materials. The influence of CMTs content on the compressive strength of GBFS-FA-CMTs cementitious system was analyzed, and the mechanism of GBFS-FA-CMTs cementitious system was also analyzed through hydration product types, physical phase composition, and microscopic morphology. The results indicated that a paste with the incorporation of CMTs, S50F30C20 (50% GBFS, 30% FA, 20% CMTs), achieved the highest compressive strength of 79.14 MPa, which was due to the filling effect of the CMTs and the degree of participation in the reaction. Pastes with different contents of CMTs, while maintaining a constant CBFS content, exhibited similar strength development. Excessive amounts of CMTs could result in reduced compressive strength. Microstructural analysis revealed that the hydration products were structurally altered by the addition of CMTs. In addition to ettringite, quartz, C(-N)-S-H gel, and calcite, gaylussite was also formed; moreover, the mass of chemically bound water increased, and the microstructure of reaction products became denser. An excess of CMTs may restrict the growth of the hydration gel, leading to more microstructural defects. The study suggests that CMTs could enhance the compressive strength of hardened paste within an alkali-activated slag-fly ash system, possibly due to a filling effect and participation in the chemical reaction. This research confirms the feasibility of using CMTs in alkali-activated cementitious materials. Full article

Granulated iron silicate slag, a by-product of pyrometallurgical copper extraction, has excellent properties for construction applications. Slag modification with CaO enhances the application properties regarding pozzolanic reactivity, potentially extending slag use in the future. The slags’ short-term leaching behavior has already been investigated with promising results, while the long-term leaching effects are less studied. Therefore, this study aims to determine the long-term leaching effects on CaO-modified iron silicate slags. The CaO-modifications were conducted during full-scale slag treatment operation. The slags were characterized and leached, and the remaining slags were investigated regarding the formation of secondary phases. The long-term leaching of main and trace elements was determined over 30 days using a dynamic leaching method corresponding to an extended time period. The leaching tests showed increased leaching of the main slag elements (Si, Ca). Zn and Cu showed peak leaching after four days of leaching, and the leaching of As and Sb decreased with the increasing CaO content in the samples. After dynamic leaching, secondary phases formed on the Cu-containing inclusions on the sample surfaces. Independent of the CaO content, the leaching of Cu was increased when subjected to external acidic and oxidating conditions using static pH titration at pH 5 in dilute nitric acid. Full article

Due to its potential pozzolanic activity, granulated copper slag (GCS) has been proven to act as a supplementary cementitious material (SCM) after thermochemical modification with CaO. This modification method reduces cement consumption and CO₂ emissions; however, the additional energy consumption and environmental properties are also not negligible. This paper aims to evaluate the economics and environmental properties of thermochemically modified GCS with CaO through the melting temperature, grindability, and heavy metal leaching characteristics. The X-ray fluorescence spectroscopy (XRF) results indicated that the composition of the modified GCS shifted to the field close to that of class C fly ash (FA-C) in the CaO-SiO₂-Al₂O₃ ternary phase diagram, demonstrating higher pozzolanic activity. The test results on melting behavior and grindability revealed that adding CaO in amounts ranging from 5 wt% to 20 wt% decreased the melting temperature while increasing the BET surface area, thus significantly improving the thermochemical modification’s economics. The unconfined compressive strength (UCS) of the cement paste blended with 20 wt% CaO added to the modified GCS after curing reached 17.3, 33.6, and 42.9 MPa after curing for 7, 28, and 90 d, respectively. It even exceeded that of Portland cement paste at 28 d and 90 d curings. The leaching results of blended cement proved that the heavy metal elements showed different trends with increased CaO content in modified GCS, but none exceeded the limit values. This paper provides a valuable reference for evaluating thermochemically modified GCS’s economics and environmental properties for use as SCM. Full article

This study aimed to investigate the environmental impact of modified granulated copper slag (MGCS) utilization in blended cement production at a representative cement plant in China. Sensitivity analysis was performed on the substance inputs, and the life cycle impact assessment (LCIA) model was applied. A detailed comparative analysis was conducted of the environmental impact of cement production in other studies, and ordinary Portland cement production at the same cement plant. Results showed that calcination has the largest contribution impact of all the impact categories, especially in causing global warming (93.67%), which was the most prominent impact category. The life cycle assessment (LCA) result of blended cement was sensitive to the chosen LCIA model and the depletion of limestone and energy. In this study, producing blended cement with MGCS effectively mitigated the environmental impact for all the selected impact categories. Results also show a reduction in abiotic depletion (46.50%) and a slight growth (6.52%) in human toxicity. The adoption of MGCS in blended cement would therefore generally decrease the comprehensive environmental impact of cement, which contributes to the development of sustainable building materials. Full article