Lower Size Fractions Research Articles

Moisture absorption rates via capillary suction within packed beds – The effect of material and fluid properties with implications for heap leaching operations

Preferential flow has been identified as a key cause for failure to meet optimal metal recovery rates in drip-irrigated leaching packed beds. In such systems, the lateral spread of solution is predominantly dependent on the strength of capillary forces within the bed. Capillary tests using the upward infiltration method were used to examine the effect of particle size distribution, porosity, wettability as well as the fluid viscosity on moisture absorption via capillary action. Tests were conducted on packed beds of different representative materials with unique physical properties: glass shards (irregularly shaped, non-porous), greywacke (irregularly shaped, porous, highly wettable) and malachite ore (irregularly shaped, highly porous, low wettability). Five size fractions were tested; 0.1–0.5 mm, 0.5–1.0 mm, 1.0–2.0 mm and 2.0–2.8 mm, including an equal mass mix of the four fractions (0.1–2.8 mm). Glycerol was used to formulate solutions with viscosities ranging from 0.8 to 2.2 cP, typical of irrigant solutions. The results indicate that particle size distribution was the main factor influencing the strength of capillary forces. However, higher levels of particle wettability and internal porosity also led to increased capillary action. A greater proportion of small to large sized pores within the beds' void networks at lower size fractions and at high porosities were deemed responsible for these effects. Increasing fluid viscosity led to slower moisture absorption rates with longer absorption times due to the higher resistance to fluid flow. The results highlight the importance of the inclusion of fines (< 1 mm particles) as well as the beneficial role high degrees of particle porosity and wettability play in aiding fluid transport via capillary action.

A Preliminary Assessment of Size-Fractionated Microplastics in Indoor Aerosol-Kuwait's Baseline.

The omnipresence of microplastic (MP) in various environmental samples, including aerosols, has raised public health concerns; however, there is presently very limited information on MPs in indoor aerosol. This paper presents a unique dataset where smaller MPs have been sampled using a six-stage cascade impactor from indoor environments in Kuwait. The MP concentration in the indoor air varied between 3.2 and 27.1 particles m−3, and the relative MP concentration decreased linearly from the lowest to the highest size fraction. A significant effect of location was observed for the total number of MPs (F2,14 = 5.80, p = 0.02) and the inhalable fraction (F2,14 = 8.38, p = 0.005), while location had no effect on the respirable fraction (F2,14 = 0.54, p = 0.60). A significant effect of the type of air conditioning used was also observed for the total number of MPs (F2,19 = 5.58, p = 0.01) and the inhalable fraction (F2,19 = 6.45, p = 0.008), while location had no effect on the respirable fraction (F2,19 = 1.30, p = 0.30). For the total number of MPs and the inhalable fraction, the concentration was significantly higher for the split unit air-conditioning as compared to the central air-conditioning plants. The presence/absence of carpets had no significant effect on the MP concentrations (total: F1,19 = 4.08, p = 0.06; inhalable: F1,19 = 3.03, p = 0.10; respirable: F1,19 = 4.27, p = 0.05). The shape was dominantly fibers, with few fragments in lower size fractions. These datasets represent the first baseline information for Kuwait, and the smaller MPs in all the samples further underscore the need to develop standardized protocols of MP collection in the ≤2.5 µm fraction that can have more conspicuous health implications.

Occurrence of Microplastic Pollution at Oyster Reefs and Other Coastal Sites in the Mississippi Sound, USA: Impacts of Freshwater Inflows from Flooding.

Much of the seafood that humans consume comes from estuaries and coastal areas where microplastics (MPs) accumulate, due in part to continual input and degradation of plastic litter from rivers and runoff. As filter feeders, oysters (Crassostrea virginica) are especially vulnerable to MP pollution. In this study, we assessed MP pollution in water at oyster reefs along the Mississippi Gulf Coast when: (1) historic flooding of the Mississippi River caused the Bonnet Carré Spillway to remain open for a record period of time causing major freshwater intrusion to the area and deleterious impacts on the species and (2) the spillway was closed, and normal salinity conditions resumed. Microplastics (~25 µm–5 mm) were isolated using a single-pot method, preparing samples in the same vessel (Mason jars) used for their collection right up until the MPs were transferred onto filters for analyses. The MPs were quantified using Nile Red fluorescence detection and identified using laser direct infrared (LDIR) analysis. Concentrations ranged from ~12 to 381 particles/L and tended to decrease at sites impacted by major freshwater intrusion. With the spillway open, average MP concentrations were positively correlated with salinity (r = 0.87, p = 0.05) for sites with three or more samples examined. However, the dilution effect on MP abundances was temporary, and oyster yields suffered from the extended periods of lower salinity. There were no significant changes in the relative distribution of MPs during freshwater intrusions; most of the MPs (>50%) were in the lower size fraction (~25–90 µm) and consisted mostly of fragments (~84%), followed by fibers (~11%) and beads (~5%). The most prevalent plastic was polyester, followed by acrylates/polyurethanes, polyamide, polypropylene, polyethylene, and polyacetal. Overall, this work provides much-needed empirical data on the abundances, morphologies, and types of MPs that oysters are exposed to in the Mississippi Sound, although how much of these MPs are ingested and their impacts on the organisms deserves further scrutiny. This paper is believed to be the first major application of LDIR to the analysis of MPs in natural waters.

Single-Pot Method for the Collection and Preparation of Natural Water for Microplastic Analyses: Microplastics in the Mississippi River System during and after Historic Flooding.

We describe a simple single-pot method for collection and preparation of natural water for microplastic analyses. The method prepares samples in the same vessel (mason jars) that they are collected in right up until the microplastics are transferred onto filters or spectroscopic windows for analyses. The method minimized contamination, degradation, and losses, while increasing recoveries and throughput when compared with conventional sieving. We applied it to surface grab samples collected from the Mississippi River and its major tributaries during and after historic flooding in 2019. Microplastics (>~30 µm) were quantified using Nile red fluorescence detection, and a small subset of samples were identified by micro-Fourier transform infrared imaging spectroscopy. Concentrations were lower during the flooding, likely due to dilution. Concentrations ranged from approximately 14 microplastics/L in the Tennessee River during flooding to approximately 83 microplastics/L in the Ohio River during low-flow (summer) conditions. Loads of microplastics tended to increase downriver and ranged from approximately 87 to approximately 129 trillion microplastics/d near New Orleans. Most of the microplastics (>60%) were in the lower size fraction (~30-90 µm) and consisted primarily of fragments (~85%), followed by fibers (~8%) and beads (~7%), with polyester, polyethylene, polypropylene, and polyacrylate as the primary microplastic types. Overall, we demonstrate that the single-pot method is effective and versatile and, because it uses relatively inexpensive and easily assembled materials, can be adapted for microplastic surveys worldwide, especially those involving sample collection by volunteers from the community and schools. Environ Toxicol Chem 2020;39:986-995. © 2020 SETAC.

Studies of a Water-Only Cyclone with a Three-Stage Cone for Fine Coal Beneficiation

ABSTRACTSeparation tests on a high-sulfur-coal sample were carried out using a water-only cyclone (WOC) with a three-stage cone (also named a tri-cone water-only cyclone). The lower size limits of deashing and desulfurization were determined to be 0.098 mm and 0.045 mm, respectively. According to a float-and-sink analysis of various size fractions in the overflow and underflow, the Ecart probable (Ep) value as well as the separation density increased as the lower size fractions decreased. According to dynamic analysis, terminal hindered-settling velocities of spherical particles in the radial direction were obtained and an equation to estimate the lower removal size limits of heavy minerals was developed. With the help of numerical simulations of water–air two-phase flow fields in a tri-cone water-only cyclone (TWOC) and a conventional hydrocyclone, the role of the three-stage cone in the separation process was analyzed.

Characteristics of molecular size fractions of humic substances derived from oxidized coal

Humic substances extracted from oxidized coal were fractionated by ultrafiltration in a MW sequence ranging from 500 to 500K. Ultrafiltered fractions were analyzed by HPSEC and IR. Results showed that ultrafiltration can efficiently fractionate an heterogeneous polydisperse humic acid (HA) into more homogeneous molecular size fractions. HPSEC provides a rapid and precise means of evaluating nominal molecular sizes of HAs. As for natural HAs, coal-derived products were found to show molecular sizes depending on both ionic strength of the medium and their properties as polyelectrolytes. Fractions of lower size range present more than one chromatographic peak whereas the higher size range fractions revealed mainly a single broad intense peak. Compositional data and IR spectra suggest that simple S and hydroxyl-rich aromatic and aliphatic compounds concentrate in the lower size fractions. Conversely, fractions of higher size range appear more complex and composed of more highly condensed structures as it is also inferred by the high C/H ratio.

Chemical effects in commercial and laboratory mixtures of ?reactive? phosphate rock and acidulated fertilisers

The chemical analyses of different size fractions of a variety of commerical and laboratory prepared samples of partially acidulated phophate rocks and mixtures of ‘reactive’ phosphate rock and single superphosphate (called LONGLIFE in New Zealand) have been studied. Whereas only minor chemical segregation effects have been observed for partially acidulated products quite a large bias has been established for LONGLIFE materials, and more especially commercial samples, where larger proportions of phosphate rock were found in the lower size fractions. This inhomogeneity was considered to arise from poor mixing of components and subsequent inconsistent granulation; more stringent rejection criteria for undersize material would greatly assist in improving the product quality. Chemical ‘deactivation’ of the phosphate rock residue in LONGLIFE materials was also observed; this can be partially explained by a selective reaction of the ‘reactive’ phosphate rock component with acid still present at the time of mixing with the single superphosphate component.