Lead Smelter Slag Research Articles

Evaluation of the remediation effect of solid waste synergistic materials on heavy metal-contaminated soil

In this study, we investigated the effect of various solid waste materials such as fly ash (CFA), steel slag, and kaolinite on the simultaneous stabilization of As, Cd, Cu, Pb, and Zn in the soil of abandoned lead-smelting slag plant. Synchronous stabilization of HMs in highly contaminated soils was achieved using the application of 29 % formulated material Fe/Ca-Si based co-remediation material (FCS) with a ratio of FeSO4 + CFA + kaolinite of 14 %: 12 %: 3 %, the bioavailable content of HMs As, Cd, Cu, Pb, and Zn was reduced by 71.55 %, 49.62 %, 91.35 %, 61.37 %, and 41.45 %, respectively, and had little effect on the pH of the soil. Leaching toxicity analyses guaranteed the safety of restorative materials. The results of the field validation experiments showed that the FCS was able to effectively reduce the content of HMs in plant rhizomes and stabilized with maintenance time. European Community Bureau of Reference (BCR) and Wenzel sequential extraction procedures showed that FCS promoted the transformation of HMs in soil from unstable to stable phases. The analysis of soil microbial community diversity by FCS showed that it created a favorable soil living environment for microorganisms and was conducive to the stabilization of HMs. SEM, Surface scanning analysis, XRD, and FTIR results showed that FCS reacts with HMs to form a stable phase. Cost analysis showed that it has certain economic benefits. In conclusion, FCS is feasible for soil remediation in lead-smelting slag-polluted areas and also provides a way for high value-added utilization of solid waste.

On The Potential Use of Copper-Modified Geopolymer Incorporating Lead-Smelter Slag for Thermal Energy Storage

Thermal energy storage (TES) system has been widely employed in concentrated solar power (CSP) plants to ensure the system efficiency. With excellent thermal characteristics, electrolytic copper powder (ECP), graphene oxide (GO) and lead-smelter slag (LSS) aggregate – a mining waste material, have been utilised in this study, aiming to fabricate metallurgical geopolymer material as a storage medium in the TES system. This paper investigated the effect of ECP contents (0, 5%, 10%, 15%, 20%) on the strength, specific heat, thermal conductivity and thermal stability of GO-engineered geopolymer mixes incorporating LSS aggregate. With 10% ECP inclusion, the flow rate and compressive strength improved significantly. Increasing ECP content improved the thermal conductivity but reduce specific heat of geopolymers. The results revealed that ECP was a promising component to be incorporated into geopolymer to enhance its physio-mechanical characteristics and thermal stability. The combination of ECP, GO and LSS to produce geopolymer materials for TES system can provide an eco-friendly solution to the CSP plants and the industry waste recovery.

Zinc Extraction from Primary Lead Smelting Slags by Oxidant Alkaline Leaching

The purpose of this work is to obtain the optimum conditions for leaching the zinc contained in an industrial lead smelting slag. In this type of slag, zinc oxide, sulfide, and ferrite are contained. Zinc extraction from these compounds consists of using a single aqueous medium, where oxidant alkaline leaching with NaOH and NaClO was used. The parameters evaluated during the experiment were as follows: percentage of solids, NaOH/NaClO ratio, and temperature. The maximum amount of recovered Zn obtained during the leaching was 58%. This percentage was achieved by using the following optimal conditions: temperature of 60 °C, 0.22 of NaOH/NaClO ratio, 10% of solids, and a reaction time of 40 min. The calculated values of activation energy confirmed that the rate-limiting step of the reaction using the decreasing particle model is diffusion. The maximum percentage of zinc obtained could only have been achieved if the zinc oxide and part of the zinc sulfide (both present in almost equal proportions in the sample) were leached into the alkaline aqueous medium in the presence of NaClO.

Incorporation of reduced graphene oxide in waste-based concrete including lead smelter slag and recycled coarse aggregate

Waste-based concrete stands as an environmentally friendly and sustainable optifon compared to conventional concrete. The waste-based concrete holds the potential to reduce the unfavorable ecological effects associated with the concrete production. In this research, along with ground granulated blast furnace slag (GGBS) and fly ash (FA) as alternative binders to cement, lead smelter slag (LSS) as sand and recycled coarse aggregate (RCA) have been utilized in the production of the waste-based concrete. The influence of reduced graphene oxide (rGO) on mechanical and durability characteristics of the waste-based concrete has been assessed. Four rGO dosages of 0%, 0.05%, 0.1% and 0.3% by weight of binder were incorporated. Scanning electron microscopy and thermogravimetric analysis were conducted to assess the rGO-reinforced concrete's microstructure. The findings indicate that rGO improves the characteristics of the waste-based concrete. 0.1% is the optimum dosage of rGO to increase the compressive strength (47%), splitting tensile strength (44%), and flexural strength (42%) and decrease the water absorption (45%) and drying shrinkage (35%) of the concrete. Further dosage leads to reduced properties of the concrete. In addition, the waste-based concrete incorporating 20% FA, 50% GGBS, 100% LSS, and 100% RCA reinforced with 0.1% rGO exhibits similar mechanical and durability properties to the conventional concrete. The enhanced performance of the waste-based concrete can be related to the reduced porosity, refined pore structure, densified hydration products and increased hydration degree of the concrete by incorporating rGO.

Innovation and performance of lead smelting slag-based multi-solid waste pavement concrete materials: Ratio design, mechanical properties, hydration products, heavy metal leaching

Lead smelting slag (LSS) is a solid waste of lead production with multiple heavy metals that can irreversibly damage natural ecosystems. Therefore, it is imperative to creatively employ LSS to promote ecologically sustainable development. In this study, LSS-ground granulated blast furnace slag (GGBFS)-cement clinker (CC)-desulfurization gypsum (DG) road cementitious materials (LSCG) were prepared by synergistically stimulating LSS using multiple solid wastes to broaden the application of LSS in road construction. Specifically, the study presents an evaluation of the optimal ratio of LSCG road cementitious materials on using an integrated weights method. The hydration process of LSCG cementitious material were determined by XRD, FTIR and SEM, and the pore size distribution and content were investigated by MIP. The results indicated that the inclusion of LSS had a detrimental effect on the mechanical strength of the mortar. LSCG cementitious materials can be manufactured to achieve satisfactory performance for medium and light-grade pavements at LSS content no more than 35%. The recommended cementitious material composition ratio for medium and light grade pavement consists of 15% LSS, 44% GGBFS, 35% CC, 6% DG and 35% LSS, 24% GGBFS, 35% CC, 6% DG, respectively. Additionally, 28d flexural tensile strength of the LSCG-based pavement concrete prepared with the above ratios reach 6.0 MPa and 5.7 MPa, respectively. XRD, FTIR and SEM analysis revealed the primary hydration products of LSCG cementitious materials consist of C-S-H gel, ettringite, portlandite, and calcite. The primary contributor to the mechanical strength of the material is the gel network that arises from the interaction between C-S-H gel and ettringite. MIP analysis revealed the progressive introduction of LSS leads to a notable rise of proportion detrimental pores and multi-hazardous pores within cementitious materials. Simultaneously, the leaching concentrations of LSCG pavement concrete for Cr, Cu, Ni, Ni, Pb, Zn, As, Mn are in accordance with the limits of the Chinese standards “GB 8978–1996″and the “GB5749–2006″. Thus, LSCG cementitious material has good environmental benefits, and application in road construction can further promote the resource utilization of LSS.

Geopolymer mortars for use in construction 3D printing: Effect of LSS, graphene oxide and nanoclay at different environmental conditions

The environmental impact of concrete 3D printing (C3DP) has become a concern due to its large cement consumption and over-exploitation of natural resources. This study investigates the viability of using geopolymer mixtures in C3DP prepared with fly ash (FA)/ground granulated blast furnace slag (GGBS) and underutilised aggregate as substitutes for ordinary Portland cement (OPC) and natural aggregate, respectively. This paper focuses on the rheological, mechanical, and shrinkage properties of FA/GGBS-based geopolymer mortar with lead smelter slag (LSS) as natural sand (NS) substitute and the impact of adding nanoclay (NC) and graphene oxide (GO), as thixotropy agents, on the yield stress development and viscosity recovery properties of the mixtures. The effect of various outdoor environmental conditions of 24 °C -50 %RH, 35 °C -90 %RH and 35 °C -50 %RH on pore water evaporation and 28-day drying shrinkage of 3D printable geopolymer mortar was studied, considering the effect of NS, LSS, NC and GO in free-formed and control conditions. LSS GO-modified mortars exhibited superior viscosity recovery capacity and yield stress evolution compared to their NC-modified counterparts. Moreover, using LSS instead of NS resulted in increased 28-day compressive strength under various environmental conditions, and LSS mortars exhibited lower drying shrinkage in both conventional casting and free-formed conditions. The findings of this paper will serve as a benchmark for further studies on the effect of different curing techniques (internal or external) on the hardened state dimensional stability of 3D printed products using alkali-activated binder systems to improve the structural integrity by controlling the water evaporation and drying shrinkage development.

Analysis of the Release Characteristics of Blast Furnace Lead Smelting Slag by Integrating Mineralogy and Dynamic/Static Leaching

Analysis of the Release Characteristics of Blast Furnace Lead Smelting Slag by Integrating Mineralogy and Dynamic/Static Leaching

Solidification of heavy metals in lead smelting slag-based cementitious materials via the hybrid binder method

The hybrid binder method offers a possible solution for lead smelting slag (LSS) disposal and the immobilization of heavy metal technologies. In this study, in order to comprehend the effects of activators, solidification/stabilization solids (S/S solids) were prepared using different activators to excite LSS. The results showed that although using a single excitation source improved the compressive strengths of S/S solids, hybrid excitation can further enhance them, which 28d compressive strength could reach 73.2 MPa and increasing by 372%. Simultaneously, the leaching concentration of heavy metals decreased significantly. The mechanisms behind the significantly improved performance of S/S solids due to hybrid excitation were discussed based on the pH value and XRD, Fourier-transform infrared, TG, scanning electron microscope, and MIP results. The increase in the alkaline component due to the introduction of different activators provided a more extensive dissolution of active substances and deeper excitation. Thereby leads to the formation of new phases with cummingtonite and the variation of phases in LSS. The use of the hybrid excitation reduces the average pore diameter and porosity to 7.71 nm and 24.35% for hardened S/S solids, respectively, and significantly solidifies the heavy metals of LSS.

Synchronous stabilization of Pb, Zn, Cd, and As in lead smelting slag by industrial solid waste

In order to prevent heavy metal (HM) pollution from lead smelting slag (LSS) to the surrounding environment, this work investigated the feasibility, influencing factors, and mechanisms of using industrial solid waste such as fly ash (FA), oil sludge pyrolysis residue (PR), and steel slag (SS) as remediation amendments. The results demonstrated that the stabilization process was influenced by the material dosage, water content, and LSS particle size. Compared to single materials, the combination amendment PR2FA1 (with a mass ratio of PR to FA as 2:1) exhibited the best stabilization effect, simultaneously reducing the leaching concentrations of As, Zn, Cd, and Pb in LSS to 0.032, 0.034, 0.002, and 0.014 mg/L, respectively. The pH value of the leachate remained between 8 and 9, which met the requirements of surface water quality class IV (GB3838–2002). Through morphological analysis, microscopic characterization, and simulated solution adsorption experiments, it was determined that the stabilization process of HMs was controlled by various mechanisms, including electrostatic attraction, physical adsorption, ion exchange, and chemical precipitation. PR2FA1 had more active components, and its fine-porous structure provided more active sites, resulting in good stabilization performance for As, Zn, Cd, and Pb. Furthermore, cost analysis showed that PR2FA1, as an environmentally friendly material, could generate profits of 157.2 ¥/ton. In conclusion, the prepared PR2FA1 not only addressed the HMs pollution from lead smelting slag to the surrounding environment but also achieved the safe and resourceful disposal of hazardous waste-oil sludge. Its excellent performance in stabilizing HMs and cost-effectiveness suggested promising commercial applications.

Development and application of lead smelting slag eco-cementitious material: Synergistic excitation regulation and heavy metal solidification

In order to realise the resource reuse and safety of lead smelting slag (LSS) that contains several harmful heavy metals, LSS eco-cementitious materials (LSSEM) were prepared in this study using calcium and magnesium sources to excite high-volume LSS (78.125%). The results show that the synergistic effect of dual excitation sources can significantly increase the compressive strength of LSSEM from 13 MPa to 34.44 MPa. Performance enhancement mechanisms were investigated using X-Ray Diffraction (XRD), Fourier Transform Interferometric Radiometer (FTIR), Thermal Gravimetric Analysis (TG), Scanning Electron Microscope (SEM), and Mercury Intrusion Porosimetry (MIP). Introduction of calcium and magnesium sources facilitated dissolution of the active components in the LSS to achieve greater excitation. Leaching experiments showed that LSSEM could significantly solidify heavy metals based on the synergistic action of the dual excitation sources. The solidification ratio for each heavy metal exceeded 70%, and the leaching of heavy metals conformed to drinking water quality standards. The slump of pavement concrete prepared with LSSEM was 130 mm, and its 28-d flexural tensile strength and compressive strength were 6 MPa and 49 MPa, respectively, meeting the requirements for pavement concrete design with light traffic load. A conceptual model of the synergistic stimulatory effect of calcium and magnesium sources on LSS excitation was developed. This study promotes solid-waste recycling and provides complementary cementitious materials with lower energy consumption and CO2 emissions for the construction industry.

Drying shrinkage of waste-based concrete reinforced with pristine graphene (PRG) nanomaterial

Drying shrinkage because of moisture loss is one of the main concerns in construction, as it can result in the creation of early cracking in concrete. This study presents the results of an experimental study on the use of pristine graphene (PRG) nanomaterial to improve drying shrinkage properties of waste-based concrete. In this study, the conventional materials of concrete are completely replaced with waste-based materials and industrial by-products including: 20 % fly ash and 80 % ground granulated blast furnace slag as binder, 100% recycled concrete aggregate as coarse aggregate, and 100% lead smelter slag as fine aggregate. Four different mixes were prepared with PRG contents of 0% (control mix), 0.05%. 0.1%, and 0.3% by the weight of binders. Drying shrinkage test (up to 28 days of curing) and scanning electron micrography (SEM) were carried out on the concrete specimens to examine the influence of the PRG concentration on the drying shrinkage properties of the concretes. The results show that increasing the PRG dosage decreases the drying shrinkage of the concrete to a minimum value which is achieved by 0.1% PRG dosage. However, it is found that beyond the 0.1% dosage the drying shrinkage increases. According to SEM analysis, this increased shrinkage is because of the agglomeration of the PRG nanomaterials at higher concentrations.

Valorization of the Zellidja Lead Smelter Slag (Eastern Morocco) in Road Building

Valorization of the Zellidja Lead Smelter Slag (Eastern Morocco) in Road Building

Development of lead smelting slag-based ecological mine backfill material: Performance control and heavy metals solidification

As the heavy metals (Cr, Ni, Cu, Zn, As, and Pb) contained in the hazardous waste lead smelting slag (LSS) can cause irreversible harm to natural ecosystems, the resourceful utilization of LSS is an urgent requirement for promoting ecologically sustainable development. In this study, multi-solid waste-excited LSS was used to prepare eco-mine cemented backfill materials (MCBM). The results show that the optimal ratio of binder composition by mass is 46% for LSS, 20% for lime ash slag (LAS), 13% for slag powder (SP), 17% for cement clinker (CC), and 4% for bischofite (BF), at which time the compressive strengths of specimens at 3, 7, and 28 days are 11.1 MPa, 16.9 MPa, and 24.2 MPa, respectively. Clearly, increasing the ratio of binder-sand will increase the compressive strength of the MCBM. The backfill slurry with a binder-sand ratio of 1:2 and a solid content of 74% has a fluidity of 259 mm and a 28-day compressive strength of 5.48 MPa, which meets the requirements for high-strength grade MCBM for self-weight backfill. The results of XRD, MIP, and SEM indicate that the hydration products are predominantly composed of CSH gels, Friedel’s salts, and other mineral phases that contribute to the strength. As the ratio of binder-sand increases, the relative proportion of harmless pores increases, the mechanical properties of the MCBM improve, the hydration products become denser, and the unclassified tailings sand (UTS) is encapsulated more effectively. According to the results of the TCLP, the solidification ratio of the MCBM for each heavy metal exceeds 70%, and the leaching of heavy metals conforms to the Chinese Class IV groundwater standard. The process is more environmentally friendly, with lower energy consumption and CO2 emissions, in line with the local government’s environmental legislation.

Historical Lead Smelting Slag Harmlessness and Valuable Metals Recovery: A Co-Treatment of Lead Slag and Zinc-Bearing Material in Rotary Kiln

The harmless treatment of historical lead smelting slag (LSS) is of significance to ecological and environmental protection, but it is still challenging in terms of the economic feasibility of alone processing due to the low content of valuable metals. Here, we performed an industrialized test with a co-treatment of LSS and zinc oxide ore in a rotary kiln to evaluate the economic feasibility and solidification effect of harmful elements. The results revealed that more than 70% of Zn and Pb were recovered from LSS in the form of dust, while the nonvolatile part of Pb, Zn, and Cd were solidified in gangue as complex silicate phases. The nonvolatile part of As came into being Fe-As intermetallic compound which was encapsulated by gangue particles or was solidified in silicate phases. The entirely enclosed structure of water-quenched slag plays an important role in the stability of slag. The TCLP and SNAL leaching tests demonstrated the high stability of water-quenched slag. A zinc oxide ore addition of 20% was recommended for energy consumption and processing capacity. Our findings highlight that the valuable metals not only can be effectively recovered but also harmful elements are solidified in gangue, providing an economical and feasible technical route for the treatment of historical LSS.

Mechanical and durability properties of natural fiber-reinforced geopolymers containing lead smelter slag and waste glass sand

• Properties of natural fiber-reinforced FA/GGBS geopolymers containing different waste-based sands (NS, LSS, and WGS) were evaluated. • Geopolymers containing WGS experienced highest strength and lowest water absorption compared to the geopolymers containing NS and LSS. • LSS modified geopolymers exhibited lowest drying shrinkage compared to the geopolymers prepared with NS and WGS. • Natural fiber-reinforced geopolymers exhibited highest strength and lowest drying shrinkage compared to unreinforced geopolymers. • Natural fibers and waste-based sands can be used to prepare sustainable and durable geopolymers for structural applications. Owing to the low tensile properties of concrete, the use of internal fibers received significant attention in concrete production. In recent years, using renewable and eco-friendly natural fibers has become a viable alternative to synthetic fibers. Toward this direction, the behavior of natural fiber-reinforced geopolymers containing industrial by-products and waste-based sands is presented in this study. Industrial by-products, namely fly ash (FA) and ground granulated blast furnace slag (GGBS), were used as binders and waste-based sands, namely lead smelter slag (LSS) and waste glass sand (WGS), were used as fine aggregates in geopolymer mortars reinforced with natural fibers (i.e., 1% coir, ramie, sisal, hemp, jute and bamboo fibers, as well as 2% ramie fiber by volume fraction of fine aggregates). The flowability, mechanical properties (i.e., compressive strength and direct tensile strength), durability properties (e.g., water absorption), and drying shrinkage of the mortars were investigated. The results reveal that, at a given binder and fiber type, geopolymers containing WGS experience higher strength and lower water absorption than those containing LSS and natural river sand (NS). LSS-incorporated geopolymers exhibit a lower drying shrinkage when compared to the geopolymers prepared with WGS and NS. It is also found that geopolymers containing 1% ramie, hemp and bamboo fiber, and 2% ramie fiber exhibit higher compressive and tensile strengths and a lower drying shrinkage than unreinforced geopolymers, with those containing 1% ramie fiber exhibiting the highest strength and lowest drying shrinkage. These findings are promising and have significant potential for the use of natural fibers in the development of structural-grade construction materials, in which binder and aggregate are replaced with industrial by-products and waste-based materials.

Solidification of heavy metals in lead smelting slag and development of cementitious materials

Lead smelting slag (LSS) is a hazardous waste containing heavy metals (Cr, Ni, Cu, Zn, As, and Pb) and its improper disposal may cause irreparable damage to the ecosystem. Cementitious materials prepared with LSS can be used in construction fields and hazardous heavy metals are also solidified in prepared cementitious materials. In this study, the effects of particle sizes of LSS (8.30, 12.54, and 19.04 μm) on the compressive strength of prepared with high-volume LSS multiple coupling excitation cementitious materials were explored. According to the composition of LSS, activators were set as 6% MgO, 6% bischofite, 7% CaO, 1% CaCl2, and 8% cement, respectively. Decreasing the particle size of LSS could significantly improve the compressive strength of cementitious materials, especially in the early stage. The sample containing LSS with the particle size of 8.30 μm showed the highest compressive strength (47.1 MPa) and activity index (78.2%) among the samples containing LSS with different particle sizes. LSS with three particle sizes was analyzed with Fourier transform infrared spectroscope (FTIR) and X-ray diffractometer (XRD). The analysis results indicated that decreasing the particle size of LSS increased the specific surface areas (SSAs) and decreased the degree of crystallinity . Moreover, the microscopic analysis of cementitious materials implied that decreasing the particle size enhanced the degree of reaction and gelation , thus resulting in the denser structure of blocks. The results confirmed the compressive strength of LSS-based cementitious materials. • Heavy metals in LSS were effectively solidified in cementitious materials. • A hydration model for LSS-based cementitious materials is proposed. • The paper presents early strength could be significantly improved with decreasing particle size. • LSS-based cementitious materials can be used in the field of prefabricated construction industrial.

Removal of arsenic in the leachate by a porous carbonaceous solid waste generated from pyrolysis of oily sludge

The leachate derived from lead smelting slag site is a potential hazard to the soil and water nearby due to its excessively high arsenic content. A porous carbonaceous solid waste (PCSW), resulting from the pyrolysis of oily sludge of tank bottom, was proposed to remove arsenic (As) from leachate. According to the results of As removal from simulated solution, PCSW can remove As efficiently and synchronously increase solution pH at equilibrium. The removal efficiency of As was 96.26% and the solution pH at equilibrium was 8.98 under the optimal conditions of PCSW dosage of 3 g⋅L−1, and initial As concentration of 12 mg⋅L−1 with the initial pH of 7.5. The adsorption rate of As was 0.319 g·(mg·min)−1, and the maximum adsorption capacity of As on PCSW was 45.314 mg⋅g−1. The removal of As from the solution was attributed mainly to the formation of stable calcium-arsenate precipitations and Fe–As complexes on PCSW surface. PCSW can also simultaneously and effectively remove the heavy metals (As, Pb, Zn, Cu, Cd) in leachate from lead smelting slag sites, and the residual concentration of all heavy metals were lower than the emission concentration (GB25466-2010, China). It is proved to be feasible for PCSW application in the treatment of leachate containing heavy metals.

Prelimitary study about use of secondary lead smelting slag in the production of asphalt mixtures

En las últimas décadas se ha presentado un rápido incremento en la producción de residuos industriales. Para la mayoría de los residuos no se encuentra un uso efectivo y causan una crisis de disposición, contribuyendo así a los problemas ambientales. Este trabajo se basa en la valoración de una escoria secundaria de plomo, como agregado en mezclas asfálticas. La escoria proviene de una industria colombiana que se dedica a la producción y comercialización de baterías de plomo-ácido. Se caracteriza por tener una forma amorfa, está compuesta por óxidos de hierro, azufre, sodio, entre otros. El objetivo del trabajo fue realizar un estudio preliminar sobre la viabilidad técnica y ambiental de la aplicación de una escoria de fundición de plomo secundario en mezclas asfálticas, con el propósito de aprovechar y darle un valor agregado a dicho residuo. Se realizó una caracterización del residuo, en cuanto, al tamaño de partícula, composición química y mineralógica; además se midieron parámetros de calidad para agregados en mezclas asfálticas, así como también se realizó el ensayo de Procedimiento de Lixiviación Característico de Toxicidad (TCLP por sus siglas en inglés) para determinar las características tóxicas de la escoria. Se observó que la escoria secundaria de plomo tiene potencial para ser utilizada en mezclas asfálticas, cumpliendo con los estándares límites de toxicidad.

Waste-based mortars containing glass powder, GGBS, lead smelter slag and foundry sand reinforced with graphene oxide

The aim of this study is to investigate the possibility of improving the mechanical properties of mortars produced with waste-based binder and sand by incorporating graphene oxide (GO) nanomaterial. Twenty-seven unique mortars were manufactured by replacing cement with glass powder (GP) and ground granulated blast furnace slag (GGBS), and river sand with lead smelter slag and foundry sand. GO was added to mortars at of 0.05% and 0.1% dosages, and flow, compression and tension tests were performed on the mortars. Scanning electron microscopy analyses were carried out to evaluate the mortars' microstructure. The results show that addition of 0.05% GO caused decreased flowability and increased in strength of the waste-based mortar. Increasing GO dosage caused a further decrease in flowability and an increase in compressive and tensile strength of mortars. Strength enhancements in the mortars from 0.05% to 0.1% GO were less significant compared to those from 0% to 0.05% GO. The scanning electron microscopy analyses revealed that mortars reinforced with 0.05% and 0.1% GO exhibited a more compact microstructure with less pores compared to the unreinforced mortars, resulting in improved properties of mortars. The results indicate a significant potential using GO in waste-based mortars for developing a new and sustainable construction material for structural applications.

Experimental Study on Lead-Smelting Slag as Paste Filling Cementing Material

Under the current pressure of mineral product price and market competition, as well as the tightening of ecological and environmental protection policies, energy saving, emission reduction and cost reduction, and efficiency increase have become inevitable trends. Lead-smelting slag of smelter, as an industrial byproduct, is harmful solid waste to be eliminated. In this research, a series of experiments on substitute for cement were done for filling cost reduction under premise of guaranteeing the filling strength, using PC32.5 cement as reference cementing material. Meanwhile, with Portland cement clinker, water quenching slag of BF ironmaking, and lead-smelting slag of smelter in different ratios, four cementing materials were made and named as cementing material I, cementing material II, cementing material III, and cementing material IV. Then, the above five cementing materials including PC32.5 cement were mixed, respectively, with tailing and water to prepare paste backfill slurry with different binder-tailing ratio and concentration. Backfill block was made and cured at 20°C; their uniaxial compressive strengths in different curing ages were measured. The result shows the strength of backfill test block using cementing material I (cement clinker and water quenching slag) without lead-smelting slag is far higher than that of test block using PC32.5 cement as cementing material. The strength of block with 16% lead-smelting slag increased dramatically, which was higher than the strength of block using PC32.5 as cementing material. However, the strength of test block decreased when the content of lead-smelting slag reached 32% and 40%. The more lead-smelting slag was added, the worse influence on strength of backfill would be. Because of large specific gravity of lead-smelting slag and low content of CaO, the hydration activity of lead-smelting slag is far lower than that of water quenching slag. Therefore, using moderate lead-smelting slag as substitute for cement will lead to increase of backfill strength and decrease filling cost.