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15 pages, 7512 KiB

Open AccessArticle

Expansive Soil Stabilization Using Alkali-Activated Fly Ash

by Huan Wang, Tengjiao Liu, Chao Yan and Jianqi Wang

Processes 2023, 11(5), 1550; https://0-doi-org.brum.beds.ac.uk/10.3390/pr11051550 - 18 May 2023

Cited by 1 | Viewed by 1389

Expansive soil swells with water and shrinks with water loss, causing serious safety problems for construction projects. This study emphasizes alkali-activated binder (NaOH excited fly ash) stabilized expansive soil. We found that swelling decreased with an increase in the amount of NaOH in [...] Read more.

Expansive soil swells with water and shrinks with water loss, causing serious safety problems for construction projects. This study emphasizes alkali-activated binder (NaOH excited fly ash) stabilized expansive soil. We found that swelling decreased with an increase in the amount of NaOH in alkali-activated binder. It was found that the alkali-activated binder stabilized expansive soils (AABS) had higher shear strength than untreated expansive soils (US), manifested by increased cohesion and friction angle. In AABS, the highest cohesion and the highest shear strength were found when the NaOH mass was 6% of the fly ash mass. The strength of AABS was similar to that of US without curing. AABS had higher strength than US after 7 and 14 days of curing. The unconfined compressive strength increased with extension of curing time. Combined with XRD and SEM analysis, it was shown that the mechanism of AABS was the formation of C–S–H and (C,N)–A–S–H and the change in the internal structure of expansive soil. This investigation can solve both the expansive soil problem and provide new concepts for green development. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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11 pages, 4699 KiB

Open AccessArticle

Mechanisms of Separation and Crystal Growth of Mullite Grains during Preparation of Mullite-Based Ceramics from High Alumina Coal Fly Ash

by Jianbo Zhang, Huiquan Li and Shaopeng Li

Processes 2022, 10(11), 2416; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10112416 - 16 Nov 2022

Cited by 1 | Viewed by 1212

Abstract

High-alumina coal fly ash (HAFA: 45% Al₂O₃ and 40% SiO₂) is regarded as a special solid waste that is generated from power plants in northwestern China. It is regarded as an important substitute for bauxite and is applied [...] Read more.

High-alumina coal fly ash (HAFA: 45% Al₂O₃ and 40% SiO₂) is regarded as a special solid waste that is generated from power plants in northwestern China. It is regarded as an important substitute for bauxite and is applied to prepare mullite-based ceramics. In this work, a hydrometallurgy–pyrometallurgy synergistic process is proposed to resolve the lower Al₂O₃/SiO₂ mass ratio (Al/Si) and lower degree of crystallinity that can promote the formation of compact mullite-based ceramics. During the activation–desilication process, the inert Al-O-Si is activated to form more active Si-O-H in acid activation, which can be decomposed easily in the desilication process, and the Al/Si mass ratio increases from 1.17 to 2.80, so the mullite grains and metastable phase can be exposed. During the sintering process, mullite grains and the metastable phase tended to axial growth, part of the metastable amorphous Q⁴(3,2,1Al) structure was transformed to Q⁴(4Al) structure (mullite), and then the staggered spatial structure was formed such that the bulk density and apparent porosity of the mullite-based ceramic reached 2.85 g/cm³ and 0.5%, respectively. This process not only consumes more HAFA but also helps alleviate the shortage of bauxite, which will promote the development of clean coal-fired power generation. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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12 pages, 2234 KiB

Open AccessArticle

Laboratory Research on Design of Three-Phase AC Arc Plasma Pyrolysis Device for Recycling of Waste Printed Circuit Boards

by Liuyang Bai, Wenbin Sun, Zhao Yang, Yuge Ouyang, Min Wang and Fangli Yuan

Processes 2022, 10(5), 1031; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10051031 - 22 May 2022

Cited by 4 | Viewed by 2043

Abstract

Accumulation of electronic waste (e-waste) will place a heavy burden on the environment without proper treatment; however, most ingredients contained in it are useful, and it could bring great economic benefits when recycled. A three-phase alternating current (AC) arc plasma pyrolysis device was [...] Read more.

Accumulation of electronic waste (e-waste) will place a heavy burden on the environment without proper treatment; however, most ingredients contained in it are useful, and it could bring great economic benefits when recycled. A three-phase alternating current (AC) arc plasma pyrolysis device was designed for resourcing treatment of waste printed circuit boards (WPCBs). This paper focuses on the analysis of plasma pyrolysis gas products, and the results showed that the plasma could operate stably, and overcame the problems of the poor continuity and low energy of single-arc discharge. Air-plasma would generate NO_x contaminants, burn the organics, and oxidize the metals; therefore, air had not been selected as a working gas. Ar-plasma can break the long chains of organic macromolecules to make a combustible gas. Moreover, the strong adhesion between the metals and fiberglass boards would be destroyed, which facilitates subsequent separation. Ar/H₂-plasma promoted the decrease of carbon dioxide and the increase of combustible small molecular hydrocarbons in the pyrolysis product compared with Ar-plasma, and the increase of the H₂ flow rate or plasma power intensified that promotion effect. The percentage of other components, except the hydrogen of CO₂, CO, CH₄, C₂H₄, and C₃H₆, accounted for 55.7%, 34.2%, 5.6%, 4.5%, and 0% in Ar-plasma, and changed to 35.0%, 29.0%, 11.2%, 24.3%, and 0.5% in Ar/H₂-plasma. Ar/H₂-plasma could provide a highly chemically active species and break chemical bonds in organic macromolecules to produce small molecules of combustible gas. This laboratory work presents a novel three-phase AC arc plasma device and a new way for recycling WPCBs with high value. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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23 pages, 6686 KiB

Open AccessArticle

Design and Simulation of Small-Scale Waste Separation and Sorting Equipment

by Ziheng Xu, Jiajia Zhang and Yuhui He

Processes 2022, 10(5), 1020; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10051020 - 20 May 2022

Cited by 2 | Viewed by 4729

Abstract

Environmental pollution is currently a major concern globally owing to increase in the world population and advances in industrialization. An automatic waste separation and sorting equipment for small-scale waste sorting systems was constructed in this paper. A two-DoF (two-degree-of-freedom) parallel sorting mechanism as [...] Read more.

Environmental pollution is currently a major concern globally owing to increase in the world population and advances in industrialization. An automatic waste separation and sorting equipment for small-scale waste sorting systems was constructed in this paper. A two-DoF (two-degree-of-freedom) parallel sorting mechanism as well as a belt waste separation and feeding mechanism were designed, and 3D models of the mechanism were established. Finite element analysis (FEA) was conducted for the sorting mechanism, and kinematic and dynamic analysis and numerical simulation were performed for the waste and sorting mechanism. The simulation results demonstrated that the spherical waste did not roll out of the platform after leaving the slideway. The waste was stabilized at the center of the platform within a short duration with movement of the collecting mechanism of the platform. The system was optimized to reduce waste separation and sorting time. Stability of the waste motion in the equipment as well as efficiency of the system were significantly improved after optimization. The results showed that the designed equipment can complete separation and sorting of waste materials at lower output power. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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11 pages, 1997 KiB

Open AccessArticle

Hydrometallurgical Recovery of Iron, Nickel, and Chromium from Stainless Steel Sludge with Emphasis on Solvent Extraction and Chemical Precipitation

by Wei-Sheng Chen, Yu-Chi Chen and Cheng-Han Lee

Processes 2022, 10(4), 748; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10040748 - 12 Apr 2022

Cited by 8 | Viewed by 2940

Abstract

Stainless steel has a variety of applications nowadays because of its mechanical strength and corrosion resistance. The large-scale machinery made up of stainless steel has an outstanding performance and endurance for manufacturing industries. However, stainless steel scraps accumulate with a lubricant to form [...] Read more.

Stainless steel has a variety of applications nowadays because of its mechanical strength and corrosion resistance. The large-scale machinery made up of stainless steel has an outstanding performance and endurance for manufacturing industries. However, stainless steel scraps accumulate with a lubricant to form sludge during the operation. To reduce the environmental hazards caused by sludge, this research attempts to construct a hydrometallurgical process to recover iron, nickel, and chromium from the sludge. The experiments could be divided into four parts. First, calcination was adopted to remove the oil and water content. The factors that have impacts on the leaching efficiency, such as the type of acid and the calcination temperature, were investigated in the second part. It was optimal that the sludge was calcined at 300 ℃ for 8 h and leached by 4 mol/L HCl. The results revealed that the leaching percentages of iron, nickel, and chromium were 97.6%, 98.1%, and 95.7%, respectively. In the two-stage solvent extraction procedure, Fe(III) could be efficiently recovered by using 0.1 mol/L bis(2-ethlhexyl) phosphate (D2EHPA) at pH 1.5 with an Aqueous/Organic ratio of 1 over 10 min. The results indicated that the extraction percentage of Fe(III) was beyond 99%. Eventually, the recoveries of nickel and chromium were respectively 99.5% and 75% through chemical precipitation. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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16 pages, 3996 KiB

Open AccessArticle

Modified Activated Carbon for Copper Ion Removal from Aqueous Solution

by Wei-Sheng Chen, Yun-Chung Chen and Cheng-Han Lee

Processes 2022, 10(1), 150; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10010150 - 12 Jan 2022

Cited by 28 | Viewed by 3520

Abstract

Because of increasing environmental awareness, it is becoming more important to remove harmful elements from water solutions. This study used activated carbon (AC) derived from waste wood-based panels as the base material, oxidized with nitric acid (OAC), and grafted with iminodiacetic acid (IDA-OAC) [...] Read more.

Because of increasing environmental awareness, it is becoming more important to remove harmful elements from water solutions. This study used activated carbon (AC) derived from waste wood-based panels as the base material, oxidized with nitric acid (OAC), and grafted with iminodiacetic acid (IDA-OAC) to improve the adsorption capacity and affinity for metals. The characterization of AC, OAC, and IDA-OAC was conducted via FTIR, SEM, N₂ adsorption and desorption analysis, elemental analysis, Boehm titration, and point of zero charge (PZC). The instrument studies proved the modified increasing of the functional groups of the adsorbents. Moreover, batch and column experiments were conducted to evaluate the ability of the three adsorbents to remove copper ions from aqueous solution. In batch sorption, IDA-OAC had the highest adsorption capacity (84.51 mg/g) compared to OAC (54.74 mg/g) and AC (24.86 mg/g) at pH 5. The breakthrough point (C_t/C_i = 0.05) of copper ions for IDA-OAC occurred much later than AC in the column experiment (AC = 19 BV, IDA-OAC = 52 BV). The Langmuir isotherm and pseudo-second-model kinetics modeling could better fit with the data obtained from the batch sorption of AC, OAC, and IDA-OAC. The significant capacity and reusability of IDA-OAC displayed high applicability for water treatment. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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11 pages, 3554 KiB

Open AccessFeature PaperArticle

The Influencing Factors for Volume Stability of Ladle Slag

by Tung-Hsuan Lu, Ying-Liang Chen, Hong-Paul Wang and Juu-En Chang

Processes 2022, 10(1), 92; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10010092 - 03 Jan 2022

Cited by 2 | Viewed by 1235

Abstract

The purpose of this study was to investigate the mechanism causing the unsoundness of ladle slag. Calcination temperature may have an impact on the level of reactivity of f-CaO. When CaO was produced at a higher temperature, the reactivity of CaO was lower. [...] Read more.

The purpose of this study was to investigate the mechanism causing the unsoundness of ladle slag. Calcination temperature may have an impact on the level of reactivity of f-CaO. When CaO was produced at a higher temperature, the reactivity of CaO was lower. For example, dead burnt CaO (DCaO) was produced at higher temperatures than light burnt CaO (LCaO); therefore, DCaO had less reactivity than LCaO. In a hydration test, DCaO (1500 °C) showed 62 times lower reactivity than LCaO (900 °C), which meant that DCaO would result in the delay of hydration of CaO easily. Additionally, DCaO would cause unsoundness more easily than LCaO when adding the same number of cementitious materials. For this reason, using ASTM C114-18 (Standard Test Methods for Chemical Analysis of Hydraulic Cement) to quantify DCaO content may underestimate DCaO content by up to 20%. Conversely, this method was more suitable for f-CaO since it had high reactivity. Moreover, this study demonstrated that ladle slag would cause unsoundness when added into the cementitious material because it was produced from a higher temperature process (over 1500 °C), which generates the DCaO. Therefore, when reusing ladle slag, the problem of low reactivity of DCaO should be considered. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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12 pages, 1940 KiB

Open AccessFeature PaperArticle

Synthesis and Grafted NH₂-Al/MCM-41 with Amine Functional Groups as Humidity Control Material from Silicon Carbide Sludge and Granite Sludge

by Ya-Wen Lin, Wei-Hao Lee, Kae-Long Lin and Bo-Yi Kuo

Processes 2021, 9(12), 2107; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9122107 - 24 Nov 2021

Cited by 3 | Viewed by 1398

Abstract

Mesoporous Al/MCM-41 was synthesized by extracting silicon carbide sludge and granite sludge as the sources of silicon and aluminum. Different concentrations of aminosilane (2.5, 5, 7.5 vol.%) were used to reflux the grafted NH₂-Al/MCM-41 with amine functional groups (NH₂-Al/MCM-41). [...] Read more.

Mesoporous Al/MCM-41 was synthesized by extracting silicon carbide sludge and granite sludge as the sources of silicon and aluminum. Different concentrations of aminosilane (2.5, 5, 7.5 vol.%) were used to reflux the grafted NH₂-Al/MCM-41 with amine functional groups (NH₂-Al/MCM-41). The physical and chemical characteristics were analyzed. The results confirmed that silicon carbide sludge and granite sludge can effectively synthesize Al/MCM-41 with low cost and environmental protection. Reflow grafted amine functional groups can effectively improve the surface properties of NH₂-Al/MCM-41. The moisture adsorption and desorption capacity of grafted NH₂-Al/MCM-41 with amine functional groups was also studied. Based on moisture adsorption and desorption capacity, the surface properties of NH₂-Al/MCM-41 were studied. When 5 vol.% of NH₂-Al/MCM-41 amine functional groups is added, the moisture adsorption and desorption capacity is best. When the relative humidity = 95%, the equilibrium moisture content is 39.4 kg/kg, which complies with the standard of Japanese Industrial Standard (JIS A 1475). Therefore, the use of waste derived from the industry to replace expensive commercial materials was simple and environmentally friendly, and the grafted NH₂-Al/MCM-41 with amine functional groups can be utilized in multiple applications, particularly as moisture regulation materials in building engineering. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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Review

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15 pages, 2523 KiB

Open AccessReview

Laser Cutting Technologies and Corresponding Pollution Control Strategy

by Yingyong He, Honghu Xie, Yongjun Ge, Yishan Lin, Zhitong Yao, Binhui Wang, Meiqing Jin, Jie Liu, Xinyang Chen and Yuhang Sun

Processes 2022, 10(4), 732; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10040732 - 11 Apr 2022

Cited by 11 | Viewed by 7930

Abstract

In conjunction with the increasing demand for material cutting, such as the decommissioning and dismantling of nuclear facilities, advanced cutting technologies need be developed to increase precision and cost-effectiveness. As compared with other cutting technologies, laser cutting offers advantages of greater cutting precision, [...] Read more.

In conjunction with the increasing demand for material cutting, such as the decommissioning and dismantling of nuclear facilities, advanced cutting technologies need be developed to increase precision and cost-effectiveness. As compared with other cutting technologies, laser cutting offers advantages of greater cutting precision, accuracy, and customization. In this work, we investigated the constitution, classification, and current status of this technology. Pollutant emission during laser cutting, corresponding pollution control methods and apparatus were proposed as well. Laser cutting equipment mainly comprises an automated system integrating a fiber laser, industrial computer, servo motor control, electrical control, and detection technology. It mainly consists of mechanical and electrical control parts. Laser cutting equipment is distinguished by light source, power, and cutting dimensions. Known variants of laser cutting technology involve vaporization, fusion, reactive fusion, and controlled fracture cutting. During the cutting process, dust, smoke, and aerosols can be released, which is an environmental concern and poses a threat to public health. The selection of the dedusting method and design of apparatus should take into account the dust removal rate, initial capital cost, maintenance cost, etc. Multi-stage filtration such as bag filtration combined with activated carbon filtration or electrostatic filtration is accepted. Full article

(This article belongs to the Special Issue Advances in Solid Waste Treatment and Design)

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