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[Objective] The classification of sediment particles and the accompanying distribution characteristics of carbon, nitrogen and salt in the process of soil thawing layer by layer under snowmelt runoff scenario were analyzed in order to identify the mechanism of soil freeze-thaw erosion and the induced micro-environmental effects on eroding slopes. [Methods] Soil samples were obtained from an eroding slope in the mollisol region of Northeastern China. Air-dried soil was used to fill columns that were subjected to three treatments: non-freeze-thaw, full freeze-full thaw, and gradual progressive thawing after freezing. The soil columns were completely immersed in a water bath so that thawing occurred from outside to inside. All soil samples were then fractionated by settling velocity, and the electrical conductivity (EC), pH value, soil organic carbon (SOC), and total nitrogen (TN) of each particle size were determined and analyzed. [Results] ① The freeze-thaw process reduced the proportion of the soil particles >500 μm and ≤125 μm, but increased the proportion of soil particles between 125 μm and 500 μm. Larger particles had higher EC, but lower SOC and TN. ② Across gradual progressively thawed layers, the outer layer (thawed earlier) had fewer particles ≤63 μm, and the inner layer (thawed later) had more particles between 125 μm and 500 μm. More specifically, EC, SOC, and TN were higher in the larger fractions from the outer layer. ③ Compared with the original soil, 64.8% of the dissolved solids were lost from the soil that experienced gradual progressive thawing, but the loss rate of SOC and TN was only 4.08% and 2.72%, respectively. The loss of dissolved solids and organic matter was greater from the inner layer than from the outer layer. [Conclusion] After freezing and thawing, the degree of fragmentation of the outer layer of soil was large, and the soil particles on the slope tended to become homogenized. Organic matter content varied significantly between particle size classes, and its distribution was more stable in small-grained soils. Salts and organic matter migrated from the inner layer of the soil to the outer layer during the freeze-thaw process, resulting in loss.

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Flocculent settling widely exists in various processes of tailings disposal.It bears significance for the accurate calculation of the flocculent settling velocity in engineering, such as tailings backfilling and surface disposal.This paper studied the structural characteristics of tailings flocs from the perspective of the fractal theory, and established the mathematical relationship between tailings particle size, geometry size of floc and fractal dimension.It analyzed the influence of buoyancy effect, reflux effect and viscosity effect on floc settling, and deduced a calculation formula of tailings flocculent settling velocity.This study carried out a tailings flocculent settling test observed the changes in geometric morphology of flocs by focused beam reflectance measurement technology(FBRM), and carried out validation analysis between testing data and model calculation value.The results showed that the settling velocity increased with the equivalent grain size of flocs, which could be divided into three stages, namely accelerated settling, uniform settling and compaction settling.The equivalent grain size of flocs of test tailings were 140~350 μm, and the settling velocity calculated by the formula were 1.3~2.0 mm/s when the fractal dimension was 2.25, which demonstrates significant correlation with the testing value, and had certain practical application value.

Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Particle heterogeneity is one of the key indicators to estimate the variability in the soil properties and compositions. This study aims to explore the effects of the soil particles settling and bedding on the greenhouse gas emissions from the depositional area. The layer-specific physicochemical properties were also considered during this time. Specifically, one type of Mollisol (local people named as the black soil) was sampled from a typical eroding slope in the northeastern China. Then six classes were fractionated by their respective settling velocities. Six structures were obtained to bed the differently-sized soil particles in sequence: S1 was the thinnest structure with only > 500 μm particles L1, whereas S6 was the thickest structure with the six particle classes being layered in sequence from the coarsest particles L1 at the bottom to the finest particles L6 on top. The emissions of greenhouse gases CO2, N2O and CH4 were finally collected from the incubated structures on a daily basebasis. The results showed that: 1) The coarse particles settled first (L1) on the bottom, whereas, the fine particles settled the last and then covered on the top (L6). The porosity gradually decreased from 23.79% of coarse layer L1 to 1.0% of fine layer L6. By contrast, the soil water content increased generally at the highest moisture content of 68.78%, as the soil particles were settled with the L5. 2) Carbon and nitrogen were rich in the L2-L4 layer, where the soil organic carbon and total nitrogen were peaked in the L2 layer (with 27.34 and 2.35 g/kg, respectively), and the maximum dissolved organic carbon and nitrogen appeared in the L3 and L4 layer (with 519.31, and 19.69 mg/kg, respectively). 3) The average greenhouse gas emission rates decreased significantly during the seven incubation days, as the sedimentary layers were thicker (P<0.05). Correspondingly, there was no increase in the gas flux with the thickening of the sedimentary soil layer. The layer-by-layer deposition process was separated from the coarse and fine particles, where the coarse particles were preferentially deposited as the lower layers, while the fine ones were stacked over forming upper layers. Consequently, there was a gradual decrease trend of the porosity and relative diffusion coefficient of gas from the bottom to the top. As such, it is expected to effectively inhibit the transfer of greenhouse gases via the depositional profile. Overall, the layer-by-layer settling and bedding can be used to reconstruct the deposition process in the field, and then to effectively capture the potential impacts of depositional layer structure on greenhouse gas emissions. The finding can overcome the limitations of traditional sampling, indicating the outstanding variations of small-scale layers and bedding. The settling and bedding patterns can also be characterized to quantify the greenhouse gas emissions from different depositional settings. [ABSTRACT FROM AUTHOR]

In the future, the output of ultrafine full tailings will explode due to the massive mining of low-grade deposits and demand for the recovery of useful minerals. The best way to dispose of ultrafine full tailings is to prepare them into the paste for filling underground voids or surface stacking. The deep cone thickening of ultrafine full tailings is a key link of tailings paste disposal technology. In the thickening process of ultrafine full tailings, slow sedimentation velocity, high dosage of flocculant, excessive overflow turbidity, and low underflow concentration are the bottlenecks that restrict the application of disposal technology for ultrafine full tailings paste. To investigate the thickening characteristics of ultrafine full tailings, the sedimentation test in measuring cylinder, the small-scale and semi-industrial deep cone dynamic thickening tests were carried out. Results show that the nonionic flocculant with a molecular weight of 12 million is most beneficial for the settlement of the tailings. With increasing flocculant dosage, the turbidity of overflow decreases and underflow concentration remains unchanged. Upon increasing the solid flux, the turbidity of overflow increases and underflow concentration decreases. In particular, when the solid flux is 0.4 t·m−2·h−1, the feeding solid mass fraction is 12%, flocculant dosage is 50 g·t−1, and average solid mass fraction of the underflow of the small-scale and semi-industrial dynamic thickening test is 62.8% and 74.4%, respectively. Mud height has a significant influence on the underflow concentration. The solid mass fraction of the underflow of the deep cone thickener increases with the increasing mud height, and this process conforms to the DoseResp function. This growth process can be divided into three stages: (1) slow growth (mud height 1–4 m), (2) rapid growth (mud height 4–7 m), and (3) basic stable (mud height over 7–8 m). This is related to the compression performance of the tailings flocs at different mud heights. According to the function relation between the underflow concentration and mud height, the mud height can be adjusted to meet the required underflow concentration for underground backfilling.

The industrial aquaculture has been widely applied all around the word for its obvious benefits of eco-friendly, water-saving and good welfare conditions due to the excellent use of technology to manage aquaculture environments effectively. Water quality management, mainly composed of sedimentation, filtration, biological purification, oxygenation, temperature regulation and sterilization, is of vital importance to the aquaculture. Generally, sedimentation can be applied to deal with the water before the influence into the aquaculture tank and that after the effluent from the aquaculture tank. Most of the previous studies focused on the settling characteristics of suspended solid in the waste water from the aquaculture tank. However, few attentions are paid to that in the source of water, resulting in limited knowledge on the determination of the appropriate time required for solid sedimentation. In this study, settling characteristics and size distribution of the SS (suspended solid) in the nearshore seawater of Changzhi island, Zhoushan have been investigated by carrying out four hydrostatic settling experiments. In addition, settling apparatus with different diameters have been developed to examine the effect of apparatus diameter on the settling characteristics. Stokes equation and Mclaughlin method have been applied to calculate the settling velocity in the fourth hydrostatic settling experiments. The results show that the accumulating particle size D90 (the accumulating particle volume reaches to 90%) of suspended solids in the seawater of Changzhi island is around 45.800 μm, indicating that the suspended solids are mainly composed of silts. The mass concentration of suspended solids increases sharply with time in the first 22 min due to the quick settlement of large particles, and recoveries to the initial level after 40 min. And it continues to decreases due to the flocculating settling of small particles and reaches the level less than 40% of that in the initial samples 6-9 h later. During the final stage, it decreases slightly, stabilizing at the level of 50-60 mg/L after 12 h. Thus, the settling characteristics demonstrates that it is difficult to completely remove the suspended solids in seawater by increasing settling time and other water management strategy also should be employed. The comparisons of settling characteristics among three purpose-designed settling apparatus show that the effect of apparatus diameter can be ignored in this study. As for the settling velocity, it reaches the maximum value of near 0.01 cm/s in the early stage because of the similar reason that the large particles settle first as in the concentration analysis. In the later stage, the settling velocity decreases rapidly and becomes less than 0.001 cm/s after 6 h. Moreover, the settling velocity and concentration has been fitted in a Logistic model and the fitting equation has been obtained. The results can enrich the understanding of the settling characteristics in the source water for industrial aquaculture in Zhoushan island and provide scientific guidance on how to set up appropriate setting time for source water in settling tank. [ABSTRACT FROM AUTHOR]

To determine the characteristics of precipitation and pollutant content in storm drainage sediments, samples of sediment from building areas (including residential areas), roads, and green spaces in Wuhan were collected and analyzed. The settling velocity results show that particles with high settling velocity weight occupied a larger proportion in the sediment; the settling velocity distribution of sediments in building areas and roads was more stable than that in green spaces; and the proportion of particles with settling velocity over 3.00 cm·s -1 in building areas, roads, and green spaces decreased in turn. The particle size distribution indicated sediment size had a wide variation range, with most particles concentrated in the range 13-628 μm, and that the particle size distribution in sediment from the same land type could differ greatly. Each sample was divided into seven groups according to settling velocity. The contents of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) were tested. The results indicate that pollutant contents in groups containing particles with settling velocity over 3.00 cm·s -1 or below 0.025 cm·s -1 were lower than those in other groups. Most pollutants were concentrated in particles with high settling velocity.The COD concentration declined in green spaces, roads, and building areas, in turn, for most cases. The nitrogen content in the drainage sediment of roads was lower than those in the two other kinds of land, whereas the phosphorus content in the drainage sediment of building areas was higher than those in the two other kinds of land. In the storm drainage sediment, the ratio of COD:TN was between (51-89):1 and that of COD:TP was between (102-186):1.