Study on Photochemical Properties of a Sr-SnS2/CaIn2S4 Heterostructure to Improve Cr(VI) Removal.

Compound semiconductor photocatalysis technology is considered to be a promising treatment for solving water problems efficiently. The point of designing high-efficiency catalysts is to optimize the band gap structure and facilitate the separation of charge carriers by establishing new electron migration pathways. Recently, 3D porous CaIn2S4 was found to have good photocatalytic ability. However, the quick recombination and agglomeration of carriers still limit its application. Herein, we prepared a heterostructure by introducing 2D Sr-doped SnS2 to 3D CaIn2S4 by a hydrothermal synthesis method. The optimal dosage of Sr-SnS2 is 3%, and the photocatalytic Cr(VI) removal efficiency of 3% Sr-SnS2/CaIn2S4 (SSCS-3) is 5.82 and 10.83 times those of pure CaIn2S4 and SnS2, respectively. According to the results of characterization tests and calculation verification, we inferred that the enhanced photocatalytic removal of Cr(VI) is due to the introduction of Sr-SnS2 that can promote the rapid transfer of photogenerated electrons to the surface of CaIn2S4, and the heterostructure formed between 2D Sr-SnS2 and 3D CaIn2S4 can also provide abundant reaction sites. The promotion of carrier separation is mainly due to the formation of a built-in electric field of the Sr-SnS2/CaIn2S4 heterostructure. This work provides new ideas and technologies for the treatment of Cr(VI) in wastewater.

Immobilization enhancement of heavy metals in lightweight aggregate by component regulation of multi-source solid waste.

Integrated recycling of solid waste containing heavy metals is a critical environmental challenge. In this study, a green solution to reduce heavy metal leaching from solid waste is demonstrated by combining contaminated soil, industrial sludge and lithium slag in pairs to produce lightweight aggregates (LWAs). The physical properties and heavy metal leaching behavior of LWA samples were systematically investigated and characterized. The results showed that industrial sludge reduced the density and water absorption of LWA, while the high content of lithium slag was detrimental to the physical properties. LWA containing 80% contaminated soil and 20% lithium slag had the lowest particle density of 1.47 g/cm3 due to the hollow structure caused by the low viscosity and violent generation of SO2. LWAs with lithium slag leached excessive Cu and Cr relatively, while heavy metals were immobilized well in LWAs with contaminated soil and industrial sludge as the main components. Because the flux components of industrial sludge could enhance the encapsulation of heavy metals by glass phase. In addition, the co-immobilization of multiple heavy metals was observed in the spinel phase. This study provides an efficient and safe method for the synergistic recycling of solid waste.

Effect of Rice Husk Ash on the Properties of Alkali-Activated Slag Pastes: Shrinkage, Hydration and Mechanical Property.

In this paper, rice husk ash (RHA) with different average pore diameters and specific surface areas was used to replace 10% slag in the preparation of alkali-activated slag (AAS) pastes. The effect of RHA addition on the shrinkage, hydration, and strength of AAS pastes was studied. The results show that RHA with a porous structure will pre-absorb part of the mixing water during paste preparation, resulting in a decrease in the fluidity of AAS pastes by 5-20 mm. RHA has a significant inhibitory effect on the shrinkage of AAS pastes. The autogenous shrinkage of AAS pastes decreases by 18-55% at 7 days, and the drying shrinkage decreases by 7-18% at 28 days. This shrinkage reduction effect weakens with the decrease in RHA particle size. RHA has no obvious effect on the type of hydration products of AAS pastes, whereas RHA after proper grinding treatment can significantly improve the hydration degree. Therefore, more hydration products are generated and fills the internal pores of the pastes, which significantly improves the mechanical properties of the AAS pastes. The 28 day compressive strength of sample R10M30 (the content of RHA is 10%, RHA milling time is 30 min) is 13 MPa higher than that of blank sample.

The mechanical properties and sustainability of phosphogypsum-slag binder activated by nano-ettringite.

The cementitious material based on phosphogypsum (PG) and ground granulated blast furnace slag (GBFS) demonstrates good economy and sustainability, whereas its drawback of ultra-slow strength development seems unacceptable. In this study, an attempt to drive the hydration of PG-GBFS and further facilitate the strength development by introducing nano-ettringite (NE) was carried out. The impact of 1- 5 % NE on the compressive strength, hydration process, dissolution behavior, and microstructure evolution of PG-GBFS were investigated. The results showed that the incorporation of NE significantly increased the compressive strength of PG-GBFS. At 7 d, the strength grew from 0 MPa to a range of 7.6- 20.2 MPa, and at 28 d, it was enhanced from 22.9 MPa to a range of 45.6- 79.0 MPa. The reason was that the introduction of NE induced the formation of AFt, thereby accelerating the hydration process and promoting the development of the skeletal network, resulting in higher early strength. Besides, NE facilitated the formation of C-S(A)-H gel, which further refined the pore structure and led to continuous growth in later strength. Additionally, PG-GFBS with 5 % NE exhibited significantly lower total costs (35.0 % of NaOH-activated slag and 51.7 % of water glass-activated slag) and lower carbon emissions (30.8 % of NaOH-activated slag and 49.8 % of water glass-activated slag) at the same 28 d compressive strength, indicating its strong competitiveness in both sustainability and economy.

Assembling phenyl-modified colloidal silica on graphene oxide towards ethanol redispersible graphene oxide powder.

Recently, ethanol has shown promising potential in the large-scale reduction of graphene oxide (GO) into graphene. However, dispersion of GO powder in ethanol is a challenge due to its poor affinity, which hinders permeation and intercalation of ethanol between GO molecule layers. In this paper, phenyl-modified colloidal silica nanospheres (PSNS) were synthesized by phenyl-tri-ethoxy-silane (PTES) and tetra-ethyl ortho-silicate (TEOS) using a sol-gel method. PSNS was then assembled onto a GO surface to form a PSNS@GO structure by possible non-covalent π-π stacking interactions between the phenyl groups and GO molecules. The surface morphology, chemical composition, and dispersion stability were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, X-ray diffractometry, nuclear magnetic resonance, and particle sedimentation test. The results showed that the as-assembled PSNS@GO suspension had excellent dispersion stability with an optimal PSNS concentration of 5 vol% PTES. With the optimized PSNS@GO, ethanol can permeate between the GO layers and intercalate along with PSNS particles via formation of hydrogen bonds between assembled PSNS on GO and ethanol, achieving a stable dispersion of GO in ethanol. The optimized PSNS@GO powder remained redispersible after drying and milling according to this interaction mechanism which is favorable for large scale reduction processes. Higher PTES concentration may result in agglomeration of PSNS and formation of wrapping structures of PSNS@GO after drying and worsen its dispersion capability.

Effect of flux components of lightweight aggregate on physical properties and heavy metal solidification performance.

The preparation of lightweight aggregate (LWA) by high-temperature sintering is a promising method for recycling solid waste safely, especially for solidifying heavy metals effectively. The main aim of this research was to systematically evaluate the effects of the flux components on LWA, including Na2O, MgO, CaO, and Fe2O3. The physical properties and chromium solidification mechanism of LWA were characterized and analyzed. The results showed that the addition of Na facilitated LWA preparation and Cr solidification, whereas Ca, Mg, and Fe were deleterious to some extent. Further analysis indicated that increasing the Fe2O3 content was not conducive to the reduction of Cr because its decomposition reaction creates an oxygen-rich environment. The results of this research could provide a meaningful guide for regulating the composition of raw materials for the production of LWA to treat industrial Cr-containing solid waste.

Influence of sintering temperature on the characteristics of shale brick containing oil well-derived drilling waste.

INTRODUCTION: The influence of sintering temperature on the physico-mechanical characteristics (such as water absorption, apparent porosity, bulk density, weight loss on ignition, firing shrinkage, and compressive strength), leachability, and microstructure of shale brick containing oil well-derived drilling waste (DW) was investigated. METHODS: The experiments were conducted at a temperature ranging from 950°C to 1,050°C with 30% DW addition. RESULTS: The results indicate that increasing the sintering temperature decreases the water absorption and apparent porosity and increases the shrinkage, density, and compressive strength of sintered specimens. Moreover, the physico-mechanical properties of samples sintered at 1,050°C meet the requirements of the MU20 according to GB/T 5101-2003 (in China). The heavy metal concentrations of the leachate are much lower than the current regulatory limits according to GB16889-2008. CONCLUSION: The results from XRD and SEM show that increasing sintering temperature results in an increase of the high temperature liquid phase, which may have a significant effect on the densification process of the samples.