Electricity-driven dealkalization of bauxite residue based on thermodynamics, kinetics, and mineral transformation.

High alkalinity content of bauxite residue is a major factor that hinders resource reutilization and pollutes the environment. Although acid neutralization is a direct and effective method, the amount of acid and secondary waste of sodium salt are still difficult problems to solve. Herein, we innovatively integrated an electric field into the acid neutralization dealkalization of bauxite residue and analyzed the dealkalization behavior by thermodynamics, kinetics, and mineral transformation. The results show that the pH of the anode chamber was maintained at the acidic levels of 3-6 after 30 min of galvanostatic electrolysis, and bauxite residue can realize dealkalization by acid neutralization. In the anode chamber, Na+ was released into the leachate via the reactions of Na3Al3Si3O12 and the removal of encapsulated soluble alkali. The stainless steel wire mesh anode exhibited its superiority and decreased the Na2O content in bauxite residue from 9.48 to 3.13% through convective mass transfer driven by the electric field and steady-state diffusion under stirring. This research provides a promising method for the electricity-driven dealkalization of bauxite residue, thus facilitating the development of multifield coupling theory and the application of electric fields in the alumina industry.

An Investigation into PVA Fiber Modified with SiO2 for Improving Mechanical Properties of Oil-Well Cements.

In this paper, we conduct a comprehensive investigation into PVA fiber modified with SiO2 to improve the mechanical properties of oil-well cements. Specifically, SiO2 was coated onto the surface of polyvinyl alcohol fiber (PVAF) as its silicon source via a sol-gel process by using tetraethyl orthosilicate (TEOS), while hydrochloric acid and ammonia were respectively used as the catalyst in the sol (hydrolysis) and the gel (condensation) processes. The PVAF microstructure was then characterized with the scanning electron microscope (SEM), while the effects of the modified PVAF on both mechanical and rheological properties of oil-well cements were examined. Due to the fact that SiO2 can be uniformly coated onto the PVAF surface, such modified PVAF can slightly improve the rheology of the cement slurry, while the raw PVAF exhibits poor dispersion at a high dosage. Compared with those of cement stone without PVAF after curing for 28 days at 60 °C, the flexural strength, compressive strength, and elastic modulus of the cement stone incorporated with the modified PVAFs were enhanced by 37.7%, 66.1%, and 50.0%, respectively. The SEM test (EDX) test, XRD test, and thermogravimetric test prove that the SiO2 coating on the PVAF surface can promote the hydration of cement clinker and can react with Ca(OH)2 to generate CSH gel. The SiO2 grafted onto the surface of PVAFs can improve the bond strength at the fiber/cement matrix interface, thus improving the mechanical properties of cement stone.

Complete ammonia oxidation (comammox) at pH 3-4 supports stable production of ammonium nitrate from urine.

This study developed a new process that stably produced ammonium nitrate (NH4NO3), an important and commonly used fertilizer, from the source-separated urine by comammox Nitrospira. In the first stage, the complete conversion of ammonium to nitrate was achieved by comammox Nitrospira. In this scenario, the pH was maintained at 6 by adding external alkali, which also provided sufficient alkalinity for full nitrification. In the second stage, the NH4NO3 was produced directly by comammox Nitropsira by converting half of the ammonium in urine into nitrate. In this case, no alkali was added and pH automatically dropped and self-maintained at an extremely acidic level (pH 3-4). In both scenarios, negligible nitrite accumulation was observed, while the final product of the second stage contained ammonium and nitrate at the molar ratio of 1:1. The dominance of comammox Nitrospira over canonical ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was systematically proved by the combination of 16S rRNA gene amplicon sequencing, quantitative polymerase chain reaction, and metagenomics. Notably, metagenomic sequencing suggested that the relative abundance of comammox Nitrospira was over 20 % under the acidic condition at pH 3-4, while canonical AOB and NOB were undetectable. Batch experiments showed that the optimal pH for the enriched comammox Nitrospira was ∼7, which could sustain their activity in a wider pH range from 4 to 8 surprisingly but lost activity at pH 3 and 9. The findings not only present an application potential of comammox Nitrospira in nitrogen recovery from urine wastewater but also report the survivability of comammox bacteria in acidic environments.

Prospective association of comorbid hypertension and depressive symptoms with C-reactive protein in older adults.

BACKGROUND: Hypertension and depressive symptoms often occur together in the older population, and each has been separately linked to elevated C-reactive protein (CRP). This study investigated the prospective association between comorbid hypertension and depressive symptoms and high-sensitivity CRP (hs-CRP) in a Chinese older population. METHODS: This study used data from 4978 participants aged 50 and above, who took part in two waves (2011 and 2015) of the China Health and Retirement Longitudinal Study (CHARLS). Hypertension, depressive symptoms and hs-CRP were measured. Logistic regressions adjusted for confounding variables were used to examine the association between the baseline comorbidity of hypertension and depressive symptoms and the change in hs-CRP levels. RESULTS: Hypertension and depressive symptoms did not show independent associations with an elevated level of hs-CRP. Participants with comorbid hypertension and depressive symptoms were more likely to develop a higher level of hs-CRP at follow-up (OR = 1.39, 95 % CI: 1.12-1.74) even after adjusting for covariates. Sex- and age-stratified analyses indicated that the association between the comorbidity and higher levels of hs-CRP were prone to be observed in women (OR = 1.55, 95 % CI: 1.16-2.08) and older adults (OR = 1.74, 95 % CI: 1.20-2.52). CONCLUSIONS: Comorbid hypertension and depressive symptoms is related to a higher risk of elevated hs-CRP levels. This association appears to be more pronounced among women and older adults compared to their counterparts. LIMITATION: Depression was self-reported by participants, which might be considered less unreliable than clinical diagnoses.

Development and external validation of a quantitative diagnostic model for malignant gastric lesions in clinical opportunistic screening: A multicenter real-world study.

BACKGROUND: Clinical opportunistic screening is a cost-effective cancer screening modality. This study aimed to establish an easy-to-use diagnostic model serving as a risk stratification tool for identification of individuals with malignant gastric lesions for opportunistic screening. METHODS: We developed a questionnaire-based diagnostic model using a joint dataset including two clinical cohorts from northern and southern China. The cohorts consisted of 17,360 outpatients who had undergone upper gastrointestinal endoscopic examination in endoscopic clinics. The final model was derived based on unconditional logistic regression, and predictors were selected according to the Akaike information criterion. External validation was carried out with 32,614 participants from a community-based randomized controlled trial. RESULTS: This questionnaire-based diagnostic model for malignant gastric lesions had eight predictors, including advanced age, male gender, family history of gastric cancer, low body mass index, unexplained weight loss, consumption of leftover food, consumption of preserved food, and epigastric pain. This model showed high discriminative power in the development set with an area under the receiver operating characteristic curve (AUC) of 0.791 (95% confidence interval [CI]: 0.750-0.831). External validation of the model in the general population generated an AUC of 0.696 (95% CI: 0.570-0.822). This model showed an ideal ability for enriching prevalent malignant gastric lesions when applied to various scenarios. CONCLUSION: This easy-to-use questionnaire-based model for diagnosis of prevalent malignant gastric lesions may serve as an effective prescreening tool in clinical opportunistic screening for gastric cancer.