Acid-leaching mechanism of electroplating sludge: based on a comprehensive analysis of heavy-metal occurrence and the dynamic evolution of coexisting mineral phases

Electroplating sludge is a typical heavy metal-containing hazardous waste with tens of millions of tons produced annually in China. Acid leaching is the most common method to extract valuable heavy metals for resource recycling and environmental protection. However, the coexisting elements, which are released from electroplating sludge to the leaching solution, will hinder the recycling of valuable heavy metals. In this work, dynamic acid-leaching experiments, X-ray diffraction analysis, and simulation calculations were conducted. It was found that coexisting elements (mainly Ca, Fe, and Al) account for a large proportion, and calcium salts as coexisting mineral phase (especially CaCO3) are ubiquitous in electroplating sludge. Moreover, the evolution of coexisting mineral phase plays an essential role in the acid-leaching process: (1) the dissolution of CaCO3 contributed a strong acid-neutralization capability and released Ca2+; (2) H2SO4 is the optimal extracting reagent, since it triggered the transformation of calcium salts to CaSO4·2H2O, reducing the Ca2+ concentration; (3) the coexisting elements Fe and Al would form ferrous and aluminum salt minerals with the acid-leaching process, which reduces the leaching of low-value elements. This work provides a new perspective on the acid-leaching mechanism of electroplating sludge, where the evolution of the mineral phase effect the release of valuable heavy metals and coexisting elements. This work also provides as comprehensive information as possible on electroplating sludge and inspires the improvement of the acid-leaching method.

Energy-efficient reuse of bio-treated textile wastewater by a porous-structure electrochemical PbO2 filter: Performance and mechanism

In this work, a novel porous-structure electrochemical PbO2 filter (PEF-PbO2) was developed to achieve the reuse of bio-treated textile wastewater. The characterization of PEF-PbO2 confirmed that its coating has a variable pore size that increases with depth from the substrate, and the pores with a size of 5 μm account for the largest proportion. The study on the role of this unique structure illustrated that PEF-PbO2 possesses a larger electroactive area (4.09 times) than the conventional electrochemical PbO2 filter (EF-PbO2) and enhanced mass transfer (1.39 times) in flow mode. The investigation of operating parameters with a special discussion of electric energy consumption suggested that the optimal conditions were a current density of 3 mA cm-2, Na2SO4 concentration of 10 g L-1 and pH value of 3, which resulted in 99.07% and 53.3% removal of Rhodamine B and TOC, respectively, together with an MCETOC of 24.6%. A stable removal of 65.9% COD and 99.5% Rhodamine B with a low electric energy consumption of 5.19 kWh kg-1 COD under long-term reuse of bio-treated textile wastewater indicated that PEF-PbO2 was durable and energy-efficient in practical applications. Mechanism study by simulation calculation illustrated that the part of the pore of the PEF-PbO2's coating with small size (5 μm) plays an important role in this excellent performance which provides the advantage of rich ·OH concentration, short pollutant diffusion distance and high contact possibility.

Multidimensional dynamic regulation of cellulose coloration for digital recognition and humidity response

Structural color is an eye-catching phenomenon in nature, which originates from the synergistic effect of cholesteric structure inside living organisms and light. However, biomimetic design and green construction of dynamically tunable structural color materials have been a great challenge in the field of photonic manufacturing. In this work, the new ability of L-lactic acid (LLA) to multi-dimensionally modulate the cholesteric structures constructed from cellulose nanocrystals (CNC) is revealed for the first time. By studying the molecular-scale hydrogen bonding mechanism, a novel strategy that electrostatic repulsion and hydrogen bonding forces jointly drive the uniform arrangement of cholesteric structures is proposed. Due to the flexible tunability and uniform alignment of the CNC cholesteric structure, different encoded messages were developed in the CNC/LLA (CL) pattern. Under different viewing conditions, the recognition information of different digits will continue to reversibly and rapidly switch until the cholesteric structure is destroyed. In addition, the LLA molecules facilitated the more sensitive response of the CL film to the humidity environment, making it exhibit reversible and tunable structural colors under different humidity. These excellent properties provide more possibilities for the application of CL materials in the fields of multi-dimensional display, anti-counterfeiting encryption, and environmental monitoring.

Molecular dynamics simulation of hyaluronic acid hydrogels: Effect of water content on mechanical and tribological properties

BACKGROUND AND OBJECTIVE

Recently conducted biomedical studies have shown that the drug diffusivity of hyaluronic acid hydrogel plays an important role in the treatment of joint diseases. The drug diffusivity is closely related to the water content of hydrogel. In addition, different water content will not only affect its mechanical and tribological properties, but also change the effect of drug release.

METHODS

In this work, a Molecular dynamics simulation was used to investigate the effect of water content on spatial distribution, tribological and mechanical properties of a hyaluronic acid hydrogel network. This paper focuses on the analysis and calculation of the radial distribution function of 20, 40, 60, and 80% water content model and the friction force and mechanical parameters under the influence of different load and friction speed.

RESULTS

The results show that at 20 and 40% water content, the spatial distribution is loose and the intermolecular force is not strong, resulting in a major lack in tribological and mechanical properties; whereas at 60 and 80% water content, the spatial distribution becomes gradually compact and the intermolecular force is gradually increased. The tribological and mechanical properties manifest a marked improvement.

CONCLUSIONS

The calculations reveal that the hydrogel model has the best wear resistance, pressure resistance, and plastic deformation resistance at 80% water content. In the range of 20-80% water content, the mechanical properties and friction properties of hydrogels become better and better with the increase of water content.

Design of a simulation platform for fast neutron multiplicity counting measurements

Fast neutron multiplicity counting analysis is a new nondestructive analysis method for nuclear materials. On the basis of the basic theory of fast neutron multiplicity counting technology, an integrated neutron multiplicity simulation platform is designed and set up with the optimized combination of multiple computational tools. The platform consists of four modules: geometric modeling, particle transport, data processing and analysis, and cloud data management modules. It can implement multiple functions, such as automatic modeling, neutron transport, data visual analysis and simulation, and management of cloud platform data. Finally, simulation calculations and an experimental study of fast neutron multiplicity based on a liquid scintillator are performed with this platform. The results show that the deviation between the simulation results and the experimental results is less than 10%, and thus the simulation platform can be used for mutual inspection of mass.

Combustion and emission characteristics for a marine low-speed diesel engine with high-pressure SCR system

In order to avoid the production of sulfates and nitrates in marine diesel engines that burn sulfur-containing fuels, the operating temperature of their high-pressure selective catalytic reduction (HP-SCR) systems should be higher than 320 °C. For marine low-speed diesel engines, only the pre-turbine exhaust gas temperature can meet this requirement under specific conditions, with the main engine modulation method helping to increase the exhaust gas temperature. However, the main engine modulation method brings down the power output and fuel economy of the main engine and causes the matching problem of the turbine and the other devices with the main engine. The original engine model of the marine low-speed diesel engine and the high-pressure SCR system configuration model have been constructed using one-dimensional simulation software. In addition, the performance of the high-pressure SCR system under the conditions of low-sulfur and high-sulfur exhaust gas was thoroughly analyzed. Moreover, the two main engine modulation schemes of the scavenging bypass and the turbine exhaust bypass of the original engine matching with the high-pressure SCR system were studied. The study found that the weighted average value of the NOx under the condition of low-sulfur exhaust gas met with the requirement of the IMO Tier III regulations when the low-speed diesel engine was matched with the high-pressure SCR system. However, the weighted average value of the NOx under the condition of high-sulfur exhaust gas was slightly higher than that required by the IMO Tier III regulation. In addition, the optimal main engine modulation scheme for this low-speed diesel engine was clarified by comparing the effects of the scavenging bypass and the turbine exhaust bypass modulation on the exhaust performance, and the working performance of the original engine. With an opening of 0.4 of the CBV valve under 25% engine load, the weighted average NOx of the original exhaust gas was 3.38 g/(kW·h), the power had decreased by 0.7%, and the fuel consumption had increased by 1.0%. Furthermore, when the EGB valve opening was 0.3, the weighted average value of NOx was 3.31 g/(kW·h), the power had reduced by 2.4% and the fuel consumption had increased by 2.5%. Both modulation scheme methods made the exhaust performance of the original engine meet the requirements of the IMO Tier III emission regulations, but the scavenging bypass modulation scheme had less impact on the original engine's performance.