Zeolite-amended backfills for enhanced metals containment via soil-bentonite vertical cutoff walls

Includes bibliographical references.2016 Summer.Low hydraulic conductivity (k), soil-bentonite (SB) vertical cutoff walls are commonly used to contain contaminated groundwater in geoenvironmental applications. The low k of the SB cutoff walls is attributed, in part, to the high swelling property of the bentonite component of the backfill. In addition, the high cation exchange capacity (CEC) of the bentonite, typically on the order of 80 to 150 cmolc/kg, imparts some intrinsic attenuation capacity to the backfill for cations (e.g., metals) via cation exchange. However, due to the low amounts of bentonite in typical SB cutoff walls (i.e., < 10 % by dry weight), this attenuation capacity is limited in traditional SB cutoff walls. Therefore, consideration has been given to amending SB backfills with zeolites to enhance the attenuation or adsorption capacity. Zeolites are naturally occurring aluminosilicates with high CEC (180 to 400 cmolc/kg) and a cage-like structure that allow the zeolites to perform as a molecular sieve and as adsorbents for ammonium, heavy metals, cations, and radioactive wastewater. In this study, three types of zeolites (two types of chabazite and a clinoptilolite) were used as amendments for SB backfills to enhance the adsorption capacity with respect to two metals, viz., potassium (K) and zinc (Zn). The results of measurements of the slump, consolidation behavior, and k of the unamended and zeolite-amended SB backfills with ≤ 10 % zeolite (by dry weight) confirmed that the zeolite-amended SB backfills exhibited similar physical properties compared to those for the unamended SB backfill, including the low k (≤ 1.0×10-9 m/s) typically required for SB vertical cutoff walls. The results of batch equilibrium adsorption tests (BEATs) indicated that the added zeolite increased the adsorption capacity of the SB backfill, but the effectiveness differed for different types of zeolite and the different metals (i.e., K and Zn). The results of numerical simulations for transport of K and Zn through a hypothetical 1-m thick model cutoff wall based on the results of the BEATs indicated that the barrier containment durations increased relative to that for the unamended SB backfill by as much as 108 yr and 228 yr for backfills with 5 and 10 % zeolite amendment, respectively. Finally, the results of long-term column tests (1.05 to 3.75 yr) indicated that the retardation factor (Rd) for K with the 5 % zeolite-amended SB backfills was 2.4 to 3.2 times greater than that for the unamended SB backfill, whereas Rd for Zn was 1.4 to 2.2 times greater than that for the unamended SB backfill. Based on the results of this study, the addition of small amounts of zeolite (≤ 10 % by dry weight) to traditional SB backfills can significantly enhance the adsorption capacity of the SB backfills for metals, thereby enhancing the containment performance of vertical cutoff walls comprising zeolite-amended SB backfills. However, the magnitude of any enhanced containment is dependent on both the adsorption capacity and the adsorption behavior of the specific metal with the specific backfill, and will be dependent on both the type and amount of the added zeolite

The classification of heritage tourists: a case of Hue City, Vietnam

Heritage, especially with World Heritage status, is increasingly becoming the main attraction of many tourist destinations. Heritage tourism is also the major tourism product in Hue city, Vietnam. Hitherto, there are almost no official statistics and research pertaining to heritage tourism as well as heritage tourists in Hue. This study aims at providing a preliminary profile of heritage tourists to Hue city and identifying different categories of heritage tourists, with a special focus on package tourists. The international heritage tourists’ profile seems to be similar to official statistics of international arrivals, indicating almost no difference in socio-demographic profile between heritage tourists and general tourists in the context of Hue. Various significant differences were found between international and domestic tourists in terms of tourist characteristics, trip profile and the perception of Hue. Adopting McKercher’s [(2002) Towards a classification of cultural tourists. International Journal of Tourism Research, 4, 29–38] cultural tourist classification, five categories of heritage tourists were identified, including purposeful heritage tourists, sightseeing heritage tourists, casual heritage tourists, incidental heritage tourists and serendipitous heritage tourists. Among these, sightseeing heritage tourists and purposeful heritage tourists were dominant

Authenticity and commodification of Hong Kong heritage tourism

This study aims at examining the level of commodification and authenticity of heritage tourism in Hong Kong from a tourist standpoint. It also attempted to examine the influence of perceived commodification on perceived authenticity in the context of Hong Kong heritage tourism. Both qualitative and quantitative approaches were applied, whereas the focus was on the later one. Findings indicated a fairly authentic heritage experiences perceived by tourists. Commodification was not considered as a problem by respondents although signs of commodification were found. The findings also suggested that commodification indeed “does not necessarily” ruins the tourist’s perception of authenticity

Compressibility and Hydraulic Conductivity of Zeolite-Amended Soil-Bentonite Backfills

The effect of zeolite amendment for enhanced sorption capacity on the consolidation behavior and hydraulic conductivity, k, of a typical soil-bentonite (SB) backfill for vertical cutoff walls was evaluated via laboratory testing. The consolidation behavior and k of test specimens containing fine sand, 5.8 % (dry wt.) sodium bentonite, and 0, 2, 5, or 10 % (dry wt.) of one of three types of zeolite (clinoptilolite, chabazite-lower bed, or chabazite-upper bed) were measured using fixed-ring oedometers, and k also was measured on separate specimens using a flexible-wall permeameter. The results indicated that addition of a zeolite had little impact on either the consolidation behavior or the k of the backfill, regardless of the amount or type of zeolite. For example, the compression index, Cc, for the unamended backfill specimen was 0.24, whereas values of Cc for the zeolite amended specimens were in the range 0.19 ≤ Cc ≤ 0.23. Similarly, the k for the unamended specimen based on flexible-wall tests was 2.4 x 10-10 m/s, whereas values of k for zeolite amended specimens were in the range 1.2 x 10-10 ≤ k ≤ 3.9 x 10-10 m/s. The results of the study suggest that enhancing the sorption capacity of typical SB backfills via zeolite amendment is not likely to have a significant effect on the consolidation behavior or k of the backfill, provided that the amount of zeolite added is small (≤ 10 %)

The role of numeracy and financial literacy skills in the relationship between information and communication technology use and travel behaviour

The present research examines the role of maths-related literacies, or competencies, in influencing the relationship between ICTs and travel behaviour. We adopted a Bayesian approach to jointly model the frequency of different types of internet use, and total travel distance per traveller, with respect to measures of lifewide literacies (other than reading), specifically in the form of numeracy and financial literacy questions. Our findings revealed that participants with higher levels of these literacies used the internet more frequently, and travelled further than those with fewer skills. These literacies were directly associated with total travel distance, as well as indirectly associated through internet use. Our results therefore imply that a strong policy aim to improve maths-related literacies could have implications for mitigating the effects of social exclusion in the digital age

Low-rank Latent Matrix-factor Prediction Modeling for Generalized High-dimensional Matrix-variate Regression

Motivated by diagnosing the COVID-19 disease using 2D image biomarkers from computed tomography (CT) scans, we propose a novel latent matrix-factor regression model to predict responses that may come from an exponential distribution family, where covariates include high-dimensional matrix-variate biomarkers. A latent generalized matrix regression (LaGMaR) is formulated, where the latent predictor is a low-dimensional matrix factor score extracted from the low-rank signal of the matrix variate through a cutting-edge matrix factor model. Unlike the general spirit of penalizing vectorization plus the necessity of tuning parameters in the literature, instead, our prediction modeling in LaGMaR conducts dimension reduction that respects the geometry characteristic of intrinsic two-dimensional structure of the matrix covariate and thus avoids iteration. This greatly relieves the computation burden, and meanwhile maintains structural information so that the latent matrix factor feature can perfectly replace the intractable matrix-variate owing to high-dimensionality. The estimation procedure of LaGMaR is subtly derived by transforming the bilinear form matrix factor model onto a high-dimensional vector factor model, so that the method of principle components can be applied. We establish bilinear-form consistency of the estimated matrix coefficient of the latent predictor and consistency of prediction. The proposed approach can be implemented conveniently. Through simulation experiments, prediction capability of LaGMaR is shown to outperform existing penalized methods under diverse scenarios of generalized matrix regressions. Through the application to a real COVID-19 dataset, the proposed approach is shown to predict efficiently the COVID-19