Slurry Solids Research Articles

A novel atomistic approach of estimating interfacial free energy and growth kinetics of primary Mg2Si during semi solid slurry formation of the novel Al–15Mg2Si–4.5Si composite

A novel atomistic approach of estimating interfacial free energy and growth kinetics of primary Mg2Si during semi solid slurry formation of the novel Al–15Mg2Si–4.5Si composite

How does mine tailings slurry solids concentration affect stability of dam embankment slope?

ABSTRACT In view of many past failures of tailings storage facilities, practising engineers have been analysing current design guidelines for different elements of these facilities, including for tailings dams. In this paper, an attempt is made to investigate how varying tailings slurry solids concentration ( c s ) affects the stability of tailings dam embankment slope. To achieve this, elaborate two-dimensional limit equilibrium and finite element simulations were conducted and a steady-state seepage analysis was performed so as to obtain accurate free surface water flux through the slope. Initially, numerical analyses were performed for the downstream embankment slope when no material is retained upstream. Subsequently, with all parameters kept constant, the same slope was then checked when water is retained upstream, and finally for varying slurry solids concentration. Special attention was paid to the boundary between sedimentation and consolidation, defined as the solids concentration limit beyond which effective stresses start to develop. From the stability analyses performed, it is found that the factor of safety of embankment slope varies nonlinearly with total unit weight of the slurry. For coal tailings slurry, factor of safety reduced from 1.24 when water is retained to 1.15 when tailings slurry with c w = 60% is retained, representing a drop by 7.3%.

Influence of Battery Electrode Manufacturing Process on Electrode Characteristics and Electrochemical Performance

The numerous battery gigafactory projects show that the Li-ion battery sector is booming. Although groundbreaking technologies such as all-solid-state batteries mobilize a lot of research effort, current Li-ion liquid technology still needs to be updated. Only a few publications are related to electrode manufacturing. However, increasing the active material content, the areal capacity, or the solid slurry content is key to improve the energy density but also the manufacturing costs.The objectives of this thesis work are to understand and improve the preparation of the slurry and the manufacturing process as a whole in order to obtain the best possible performances depending on the material used. Initially, the study is carried out in an aqueous formulation for negative graphite electrodes. Still, it will be extended after that to the positive electrode in an organic formulation. The negative electrode is very interesting from a fundamental study point of view because of its specificities that limit the fast charge operation of the cells with a risk of metallic lithium deposit. This electrode's basic composition, in weight, is 96.5% graphite (90/10 mixture of natural and artificial graphite), 1.3% Na-CMC, 1.7% latex, and 0.5% electronic conductor.Eleven significant parameters were selected thanks to preliminary results and literature outcomes. Their impact is determined by crossing experiences and varying them thanks to a rational approach based on the design of experiments (DOE) methodology. A DOE is carried out to be able to study this large number of parameters with a limited number of trials. Apart from the active material and the mixer used, the parameters are grouped into three categories:- The CMC (CarboxyMethylCellulose) polymer, with the molar mass, the substitution degree, and its content.- The electronic conductors, the content as well as the nature (nanotube, nano-sphere, and platelet)- Electrode properties such as coating speed, porosity, or loading.To determine their influences, characterizations are carried out throughout the electrode coating. The slurries are analyzed by rheology and scanning electron microscopy (SEM). The adhesion of the electrodes and their structuring are measured, with particular attention on the electronic resistivity and tortuosity. Finally, the electrodes obtained are tested by electrochemical cycling at various charging rates.Tortuosity is a particularly sensitive factor in relation to the issue of rapid charge/discharge [1]. The tortuosity is measured by electrochemical impedance in the blocking and symmetric electrode configuration and corresponds to the measurement of the distance traveled by the ions in order to cross an electrode (Figure 1). [2]The results of this wide study will be presented with parameter sensitivity on capacity retention, high charging rate capabilities, or electrode mechanical properties. Interrelations between the parameters will be pointed out. Optimal electrode formulations and designs will be presented to validate the approach.[1] D. Grießl, A. Adam, K. Huber, and A. Kwade, "Effect of the Slurry Mixing Process on the Structural Properties of the Anode and the Resulting Fast-Charging Performance of the Lithium-Ion Battery Cell," J. Electrochem. Soc., vol. 169, no. 2, p. 020531, 2022, doi: 10.1149/1945-7111/ac4cdb.[2] J. Landesfeind, J. Hattendorff, A. Ehrl, W. A. Wall, and H. A. Gasteiger, "Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy," J. Electrochem. Soc., vol. 163, no. 7, pp. A1373–A1387, 2016, doi: 10.1149/2.1141607jes Figure 1

Surface Engineering Based on Conductive Agent Dispersion Uniformity: Strategies toward Performance Consistency of Lithium-Ion Batteries.

The consistency of lithium-ion battery performance is the key factor affecting the safety and cycle life of battery packs. Surface engineering of electrodes in production processes plays an important role in improving the consistency of battery performance. In this study, the drying process in the electrode manufacturing process is studied as the effect on surface engineering of the electrode materials, with consideration on impacting the battery performance. Specifically, the solid content of the slurry and drying temperature are considered to be the two factors that affect conductive agent dispersion uniformity in the porous electrodes. To achieve surface engineering on the dispersion uniformity of the conductive agent, the optimal processing parameters can be obtained by adjusting the temperature and solid content of the slurry. The mechanism of dispersion uniformity of the conductive agent is mainly related to the polyvinylidene fluoride grid structure. In the manufacturing of lithium-ion batteries, the electrode coated with 66% solid slurry and dried at 90-100 °C presents stable energy storage performance, which is beneficial to maintain the stable performance of the battery pack in the application.

Nitrogen Enriched Organic fertilizer (NEO) elevates nitrification rates shortly after application but has no lasting effect on nitrification in agricultural soils

Amidst population growth, escalating food costs, limited arable land, and farmland degradation, the adoption of innovative technologies—like organic waste recycling and nutrient recovery—is crucial for enhancing the resilience of global agri-food systems. Nitrogen-Enriched Organic fertilizer (NEO) is produced using a new method, where dinitrogen (N2) is captured from the air through a plasma process and mixed with slurries or digestates as nitrate (NO3-) and nitrite (NO2-). This process leads to solid slurry acidification and a high NO2- content, potentially yielding toxic inorganic or organic N compounds. This study investigated the impact of NEO derived from cattle slurry and biogas digestate on soil nitrification—conversion of NH4+ to NO2- and NO3- by aerobic autotrophic bacteria and archaea. We investigated and compared the potential nitrification rates in soil samples from two agricultural trials (cereal and grass) treated with NEO and other fertilizers after two consecutive fertilization years. Additionally, we examined the immediate nitrification response to NEO through 73-hour soil incubations. Our results revealed that NEO significantly stimulated nitrification rates in agitated soil slurries, regardless of the feedstock used, surpassing rates observed in ammonium controls. Similarly, this pattern was also observed in loosely placed soil samples, with high nitrification rates occurring with NEO and ammonium chloride. Interestingly, the differences in nitrification rates between field-fertilized soil samples were minimal and inconsequential, suggesting that while NEO exhibits a rapid boost in nitrification rates shortly after application, this effect is not sustained ≈ six months after fertilization under field conditions. Consequently, NEO indicates its potential as an environmentally benign fertilizer without adversely affecting soil nitrification.

Fabrication of hierarchical lattice structures from zirconia stabilized ceramics by micro-SLA 3D printing approach

The need for the new materials and advanced manufacturing techniques for achieving the highest characteristics of energy devices is an obvious trend. One of the possible ways to create structures for energy applications is to introduce complex geometries and promising features with additive manufacturing (AM). Using this approach, it is possible to create complex geometry and moreover decrease the weight of materials. In this paper, we developed the layer-by-layer fabrication approach of ceramic hierarchical lattice structures via the (micro-SLA) technology. As a feedstock material, the novel composition of partly stabilized-zirconia ceramics (6ScSZ, 8YSZ) was developed. Materials were selected as a solid slurry component due to high ionic conductivity at the working temperature of modern solid oxide fuel cells (SOFCs). For the sintering, the green body heat treatment process was optimized to one step, which decrease the time and production cost. The data from scanning electron microscopy and micro-CT shows that 112-layer samples of the octet truss did not show any critical defects, and the achieved relative density was close to the theoretical one. Totally, 22 samples with the total size of 6.5 mm * 6.5 mm * 2.8 mm and the diameter of struts in the range of 240–250 μm were fabricated at a rate of only 56 min per sample, using two modifications of advanced doped zirconia-ceramics. This study opens new opportunities for the development and transfer to the production of additive manufacturing of ceramics to build energy systems devices such as solid oxide fuel cells.

Industrial Scale Testing and Evaluation of Silver Recovery Process

In this paper an industrial scale testing and evaluation of a silver recovery process for treating silver-containing materials is presented. The process that is based on the thiourea leaching, followed by silver cementation allows for recovery of the majority of silver as a metallic product. The thiourea leaching was developed specifically for the zinc cake residue, produced from the conventional zinc roast-leaching process at the KCM 2000 AD (Bulgaria), which contains up to 200 g/t silver. The material has a complex zinc ferrite dominated mineralogy with minor zinc hydrosulfate, gypsum, anglesite and plumbojarosite. The feed zinc cake residue is washed with water to remove water soluble zinc by pulping it into 25-30% solids slurry. The washing is carried out in 60 minutes and the resulted slurry is sent to the solid/liquid separation section for filtration. The resulted solids are sent to thiourea leaching and the zinc-containing solution is sent for further zinc recovery. The washed (water-soluble zinc free) solids is pulped into 20% solids slurry. Using thiourea as lixiviant, ferric iron as oxidant, sodium metabisulfite as a reductant and sulfuric acid for pH control, the leaching is performed for 35 minutes at 35oC. Within the leaching process the operating conditions are controlled to allow high silver extraction, while reducing the detrimental effects of thiourea degradation. Silver is recovered from the pregnant leach solution by cementation that results in the formation of a high-grade silver cement product. Iron powder is used as a cementation agent to recover over 94% silver at ambient temperature for 90 minutes. Details of the development work and key process steps are described. The operational data and outcomes of the industrial scale testing are presented along with process performance evaluation.

Effect of pretreatment on Typha biomass for biogas production

Plant biomass as an alternative energy source serves as a viable option for improving sustainable development and reducing greenhouse gas emissions. However, the tight bonding within its constituents may hinder anaerobic digestion, thus, requires pretreatment to break down the complex polysaccharide structure into simpler disaccharide and monosaccharide sugars to facilitate digestion and enhance the production of biogas. The research determined the effect physical and chemical pre-treatment methods of Typha biomass for biogas production. Characteristics determined include; carbonnitrogen (C-N) ratio for Typha biomass, temperature, pH, total solids (TS) and volatile solids (VS) of slurry formed by mixing the biomass with cow-dung in ratio 1:1. The volume of biogas produced was determined by water displacement method using an anaerobic digester while the mass balance approach was used to estimate the biogas yield from the TS/VS lost. Results indicated 31.6 C-N ratio; pH of 6.7; Temperature of 32.4OC and TS of 11.3%, which falls within suitable ranges reported for biogas production. The volume of biogas produced was 180 cm3, 235cm3 and 118cm3 for control, physical and chemical pre-treated samples respectively. Similarly, the biogas yield was 21mg/l, 15mg/l and 48mg/l for control, physical and chemical pre-treatment respectively. Hence the findings revealed physical pre-treatment as the best pretreatment method for biogas generation from Typha biomass in relation to chemical pretreatment and untreated Typha biomass.

Effect of process variables and melt treatment conditions during cooling slope semi solid slurry generation process of Al-7Si-0.3 Mg alloy

Simulation studies on semi solid slurry preparation of A356 alloy employing cooling slope technique, with the help of an existing multiphase and multiscale model, are presented here. The constituent phases considered in the multiphase model are the liquid melt of A356 alloy, near spherical primary Al grains, and air. The numerical study features prediction of slurry morphology, for a desired set of process conditions of cooling slope slurry formation technique. In particular, the effects of melt pouring temperature into the slope, slope angle variation and addition of grain refiner and modifier within the melt on the thermophysical and morphological properties of the generated slurry are studied. Attempts are made to gain insight into the transport phenomena of cooling slope slurry generation process, with respect to volume fraction of constituent phases, morphological evolution of solidifying primary Al grains, viscosity distribution, temperature field, velocity field, macro and micro segregation, and isothermal coarsening kinetics of α-Al grains. The efficacy of the multiphase model is validated by performing relevant experiments.

Preparation of Cemented Carbide and Study of Copper-Accelerated Salt Spray Corrosion and Erosion Behavior.

(1) Mud pulser carbide rotors, as a core component of ground communication in crude oil exploration, are often subjected to mud erosion and acid corrosion, resulting in pitting pits on the surface, which affects the accuracy. The purpose of this study was to investigate the acid corrosion and erosion behavior of cemented carbide materials and provide a reference for the wider application of cemented carbide materials in the petrochemical industry. (2) Experimental samples of tungsten–cobalt carbide were sintered at a low pressure by powder metallurgy. The petrochemical application environment was simulated by accelerated salt spray corrosion and solid slurry erosion with the aid of acidic copper, and the experimental phenomena were analyzed by SEM (scanning electron microscope), EDS (Energy Dispersive Spectroscopy), and XRD (X-ray diffraction). (3) The experimental results show that the coercivity of the pitted cobalt-cemented tungsten carbide prepared in this study was 17.89 KA/m, and the magnetic saturation strength was 14.42 G·cm3/g. The corrosion rate was the fastest during the acidic copper acceleration experiments from 4 h to 16 h, and the corrosion products of WCo3 and Co3O4 were generated on the corrosion surface. The maximum erosion rate of 0.00104 in the erosion experiment corresponds to a corrosion sample with a corrosion time of 36 h. (4) Therefore, the coercive magnetic force and magnetic saturation strength could be derived from the prepared carbide hard phase grains and carbon content in the appropriate range. The corrosion product in the corrosion process slowed the corrosion rate, and a large amount of cobalt and a small amount of tungsten was lost by oxidation during the corrosion process. The corrosion time had the greatest effect on the erosion performance of the carbide, and the long corrosion time led to surface sparseness, which reduced the erosion resistance.

Effect of drag models on hydrodynamic behaviors of slurry flows in horizontal pipes

The Eulerian–Eulerian method is efficient when dealing with liquid–solid slurry flows containing a large number of particles, but its reliability relies on an accurate description of liquid–particle interaction for which numerous interphase drag models have been proposed. However, the performance of these models has not been systematically evaluated when applied to slurry flows. In this study, slurries in horizontal pipes under various flow conditions are simulated using the Eulerian–Eulerian method. Six commonly used drag models, such as the Schiller–Naumann, Wen–Yu, Gibilaro, Gidaspow, Syamlal–O'Brien, and Huilin–Gidaspow models, are assessed based on their predictions of streamwise velocity, secondary flow, solid concentration, and liquid turbulent kinetic energy. Under normal operations, all models provide similar streamwise velocities and secondary flow patterns. However, the Schiller–Naumann model presents an intensified secondary flow and a flattened solid concentration profile. All models perform poorly for the solid concentration distribution, which may be corrected by considering the overall mean solid concentration. Additionally, the Wen–Yu model, which has previously been thought applicable only for dilute systems, behaves very closely to the Gidaspow model, which is usually recommended for dense fluidized beds.

Thermally insulating magnesium borate foams with controllable structures

In this study, a manageable foam-casting technique for preparing novel magnesium borate foams (MBFs) with highly controllable performances is presented. MBFs were prepared using MgO and boric acid as the primary materials, with different amounts of foaming agents, thickening agents, and solid slurry contents. The results showed that the MBFs possess compressive strengths (0.74–11.32 MPa), low thermal conductivities (0.171–0.976 W/(m·K) at 200–800 °C), and high porosities (51.78–80.70%). Therefore, they can serve as novel architectural materials for heat preservation and partial load-bearing applications.

A generic environmental risk assessment framework for deep-sea tailings placement

Deep-sea tailings placement (DSTP) involves the oceanic discharge of tailings at depth (usually >100 m), with the intent of ultimate deposition of tailings solids on the deep-sea bed (>1000 m), well below the euphotic zone. DSTP discharges consist of a slurry of mine tailings solids (finely crushed rock) and residual process liquor containing low concentrations of metals, metalloids, flotation agents and flocculants. This slurry can potentially affect both pelagic and benthic biota inhabiting coastal waters, the continental slope and the deep-sea bed. Building on a conceptual model of DSTP exposure pathways and receptors, we developed a stressor-driven environmental risk assessment (ERA) framework using causal pathways/causal networks for each of eight pelagic and benthic impact zones. For the risk characterisation, each link in each causal pathway in each zone was scored using four levels of likelihood (not possible, possible, likely and certain) and two levels of consequence (not material, material) to give final risk rankings of low, potential, high or very high risk. Of the 246 individual causal pathways scored, 11 and 18 pathways were considered to be of very high risk and high risk respectively. These were confined to the benthic zones in the mixing zone (continental slope) and the primary and secondary deposition zones. The new risk framework was then tested using a case study of the Batu Hijau copper mine in Indonesia, the largest DSTP operation globally. The major risk of DSTP is smothering of benthic biota, even outside the predicted deposition zones. Timescales for recovery are slow and may lead to different communities than those that existed prior to tailings deposition. We make several recommendations for monitoring programs for existing, proposed and legacy DSTP operations and illustrate how georeferenced causal networks are valuable tools for ERA in DSTP.

Cactus Cladode Juice as Bioflocculant in the Flocculation-Thickening Process for Phosphate Washing Plant: A Comparative Study with Anionic Polyacrylamide

In the phosphate industry, the thickening process is vital to increasing the solid slurry concentration and to recovering water that is as clear as possible. The performance of the thickening process depends mainly on the coagulation–flocculation effect. The thickening process is based on flocculant agents to concentrate particles: flotation and washing plant rejects as large flocs, which accelerate their sedimentation velocity. The phosphate industry worldwide uses synthetical flocculants such as polyacrylamides. These flocculants are non-biodegradable, limiting the process efficiency regarding cost and harmful effects on the environment. This study proposes cactus cladodes juice as an eco-friendly alternative to industrial flocculants. The particle size of the phosphate samples ranges from 0 μm to 160 μm, with a solid concentration of 8%. This bioflocculant allowed for an increase in sedimentation velocity of 95% compared with the case without flocculant. The optimal amount of cactus bioflocculant for decanting 1 tonne of phosphate pulp at pH 7–8 is 1.12 kg. Special attention is paid to understanding the flocculation mechanism. The results of the physicochemical characterization show that the flocculant biopolymers have similar characteristics to anionic polyacrylamide. This work indicates the promising application of the cactus juice bioflocculant in phosphate washing plants.

Effect of the modification of spray drying parameters on the fabrication of bovine-derived hydroxyapatite microspheres for biomedical applications

In this work, the effect of the spray dryer parameters on bovine-derived hydroxyapatite (BHAp) was studied to fabricate microspheres with controlled particle size distribution and morphology. A factorial design was implemented to establish the impact of spray drying process parameters on the final BHAp powder properties. The critical process factors were solid content in the slurry, atomization pressure, and hot air flow rate, whereas the studied experimental outputs were particle size distribution and morphology, characterized by laser diffraction and scanning electron microscopy, respectively. Additionally, the Ca/P molar ratio was evaluated from X-ray diffraction data. The obtained results showed a strong influence of the atomization pressure and the solid slurry content on the particle size distribution (increasing from 2.56 ± 0.02 µm to 32.46 ± 0.78 µm) and particle morphology (with an increased circularity from 0.3502 ± 0.0172 to 0.8688 ± 0.0039), being both properties suitable for thermal spray (TS) applications. Moreover, the BHAp crystalline structure and Ca/P molar ratio did not present any changes with the spray drying process parameters employed. Finally, it was found that magnesium was preserved in the spray dried particles, the former being also present in the starting powder feedstock.

Encapsulation of Orange Oil Using Fluidized Bed Granulation.

The primary objective of this research is to determine how granulation compares to spray drying/agglomeration for producing larger, more dense flavoring particles. Granulation can yield large, dense particles and thereby negate the need for a two-step process (spray drying followed by agglomeration) to achieve improved flow/handling properties of dry flavorings. In this study, a 55% solids slurry (blend of OSAn-modified starch and maltodextrin 15DE) was prepared and then single-fold orange peel oil was added at 20 or 25% of the carrier solids level. The 20% flavoring emulsion was spray dried (SD), and a portion of the resultant powder then agglomerated (Agg) in a bottom spray, fluidized bed. A second emulsion of the same carrier composition but using 25% orange oil based on carrier solids was prepared and subjected to fluidized bed granulation (FBG). Particle size, density, orange oil retention and oxidative stability on storage were determined. Overall, it is observed during this study that FBG produces orange oil encapsulates that possess better properties, such as more resistance to oxidation, a better retention of orange oil and a higher density than SD or SD/Agg powders.

Mathematical Model for Rice (Oryza Sativa) Growth Analysis Under Green Fertilizer of Biogas Slurry

The purposes of this study were to observe and measure the growth of rice plants against the application of biogas slurry fertilizer, to calculate the growth rate of rice plants with an appropriate mathematical model, and to recommend a dose of biogas slurry fertilizer for rice cultivation. This study was conducted in an experimental field using plant pots with 5 treatments of applying biogas slurry, namely without treatment/control (K), 60 Mg/ha of liquid slurry (C1), 30 Mg/ha of liquid slurry (C2), 60 Mg/ha of solid slurry (P1), and 30 Mg/ha of solid slurry (P2). Each treatment was repeated 2 times with each plant pot filled with 3 rice plants. The pots were set in randomized complete block design. The growth parameters observed were the number of leaves, plant height, number of tillers, crown weight, and plant root weight. Observations were made for 120 days. The analysis used in this study used one-way ANOVA analysis, linear regression and logistic equation for plant growth rates. The results showed that the P1 treatment had the best growth response. The coefficient value of plant growth rate (μ) on the number of leaves treatment parameters K, C1, C2, P1, and P2 were -0.044; -0.047; -0.0567; -0.0613; and -0.0547, respectively. Then, the plant height parameters were -0.0448; -0.0474; -0.0448; -0.0421; and -0.0458, respectively. The number of tillers in a row were -0.0408; -0.0405; -0.0432; -0.0447; and -0.0448, respectively. The ANOVA test showed that the application of biogas slurry fertilizer was significant (sign < 0.05) on plant growth rate, while it had no significant effect on wet and dry weight of shoots and plant roots (sign > 0.05). Logistic equation was excellent to describe rice growth under biogas slurry fertilizer. The dose of slurry biogas fertilizer that provides the most contact for plants was 60 Mg/ha.

A study of the thickening process for fine tailings of gold-bearing ores

Refractory low-grade gold-bearing ores require deep processing with finer preliminary grinding. As a result, finely dispersed products are formed, including fine tailings, which raise particular environmental concerns. The article presents the results of experimental thickening studies for the concentration tailings of gold-bearing ores from the Yuzhno-Nevyanskoe and Panovskoe deposits. The material studied is distinguished by the presence of fine clay inclusions, which reduce the sedimentation rate of slurry solids. The main processing methods are gravity separation in centrifugal concentrators and flotation. Electrokinetic properties of the particle surface, in particular, the x-potential, in the tailings slurries entering the thickening process may be used to predict thickening performance with sufficient accuracy and significantly reduce the number of laboratory experiments. Measured values of the x-potential, electric double layer thickness, and other dielectric properties of the particle surface were used to establish that the most effective sedimentation of the tailings was achieved at a mass fraction of solids in the slurry of up to 25 % and a pH value of at least 10.5. The optimal flocculant feed amount required to increase the slurry sedimentation rate was also established. It is therefore recommended to use the following flocculants for the ore processing tailings of the Yuzhno-Nevyanskoe deposit: Praestol 2510 at more than 10 g/t and Magnaflok 10 at over 20 g/t. Flocculants are not required for thickening the ore processing tailings of the Panovskoe deposit.

Frustrated Coulombic and Cation Size Effects on Nanoscale Boehmite Aggregation: A Tumbler Small- and Ultra-Small-Angle Neutron Scattering Study

To better understand the effects of solution chemistry on particle aggregation in the complex legacy tank wastes at the Hanford (WA) and Savannah River (SC) sites, we have performed a series of tumbler small- and ultra-small-angle neutron scattering experiments on 20 wt % solid slurries of nanoparticulate aluminum oxyhydroxide (boehmite) with M1+ nitrates of various concentrations and radii. The solutes consisted of H, Li, Na, K, and Rb nitrates at 10–5, 10–3, 10–1, 2, and 4 molal (m) concentrations, as well as in pure H2O. Synthetic boehmite nanoparticles were used with a size range from ∼20 to 30 nm. Tumbler cells were used to keep the solids from settling. Although particles initially form individual rhombohedral platelets, once placed in solution, they quickly form well-bonded stacks, primary aggregates, up to ∼1500 Å long, and a second level of aggregates whose concentration and structure vary as a function of cation type and concentration. Aggregation generally increases with increased solute concentration and with cation radius up to a concentration somewhat above 10–1 m, at which point the trend reverses. Primary aggregates become more rodlike and larger. The Kirkwood-like reversal probably reflects a change from Derjaguin–Landau–Verwey–Overbeek (DLVO)/Debye behavior controlled by surface chemistry to a frustrated Coulombic system controlled by the solution structure. These data suggest that an understanding of the effects of salt concentration and chemistry on nanoparticle aggregate structures provides useful physical insights into the microscopic origin of slurry rheology in the Hanford and Savannah River legacy wastes.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study.

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu2+, Cd2+, and Pb2+. The temperature (423K) and time (1.5h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60min and showed an adsorption capacity of 26.84mg/g, 24.79mg/g, and 23.86mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu2+, Cd2+, and Pb2+, respectively, at 310K and pH 6 with an initial concentration of 150mg/L. The adsorption process followed a pseudo second-order model with an R2 value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu2+, Cd2+, and Pb2+ respectively after 5 consecutive cycles.