Solid-liquid Separation Characteristics Research Articles

Significantly enhanced sedimentation and adsorption of clay materials by plasma-initiated polymerization

Except for the high adsorption capacity, the color of the adsorbent suspension and the solid-liquid separation characteristics are also essential factors for adsorption material in wastewater management. Here, a novel carboxymethyl chitosan grafted magnetic montmorillonite (CMC@MMt) adsorbent-material with large metal ions uptake capacity, transparent solution, excellent turbidity, and low cytotoxicity in human hepatic cells (HepG2 cells) was successfully synthesized by plasma technology. The adsorption performance for different metal ions, the turbidity property, and the toxicity of CMC@MMt were evaluated by systematic studies. The results indicate that adding of CMC could enhance the adsorption capacity because of NH2, COOH, and OH functional groups. Especially the turbidity property of montmorillonite was also improved due to the enlarged grain size and the polarity reduction. This research will promote the application of clay mineral-based material in environmental pollution control, such as preconcentration and immobilization of heavy metal ions.

Methyl silicate promotes the oxidative degradation of bisphenol A by permanganate: Efficiency enhancement mechanism and solid-liquid separation characteristics

Permanganate (Mn (VII)) is an environmentally-friendly mild oxidant in the field of advanced oxidation treatment, however, manganese colloids are produced as byproducts, which is difficult to separate from water, resulting in secondary pollution. This study used potassium methyl silicates (PMS) as surface modifiers to improve the aggregation of colloidal particles by increasing the hydrophobicity of the colloidal surface, and then explored the oxidation of bisphenol A (BPA) by Mn (VII) under the influence of potassium methyl silicate and the solid-liquid separation performance of the reaction system. The results showed that PMS and sodium silicate (SS) substantially enhanced the degradation of BPA by Mn (VII), and the promotion effect of potassium methyl silicate was greater than that of sodium silicate. PMS provided not only enough adsorption sites for MnO2 colloidal particles formed in the reaction process, but also reaction space for Mn (VII) to catalyze the oxidation of BPA. PMS combined with the hydroxyl group of MnO2 through hydrogen bonds and forms hydrophobic PMS-MnO2 complexes which accelerated sedimentation by polycondensation. The strong adsorption ability of in situ formed MnO2 colloids also accelerated the deposition of PMS-MnO2 complex. This study solved the low efficiency problem of Mn (VII) oxidation degradation of organic pollutants and difficult separation of manganese containing colloids and provided a new strategy for the efficient utilization of Mn (VII).

Efficient separation of zinc from zinc containing copper sulfide concentrate by chemical leaching

As the most abundant copper containing resource and zinc containing resource, chalcopyrite and sphalerite/marmatite commonly coexist as Cu-Zn mixed ores in deposits. However, it is difficult to completely separate sphalerite and chalcopyrite by flotation, thus resulting in the existence of zinc impurity in copper concentrate. Sphalerite/marmatite existed in copper sulfide concentrate as impurity may lead to severe damage of the smelting equipment, and cause the waste of copper and Zn resources, it will also decrease of the sale price of copper concentrates. Therefore, the deep separation of zinc from zinc bearing copper sulfide concentrate is of great significance. In this work, selective chemical leaching was developed to efficiently remove zinc from zinc containing copper sulfide concentrate. Under the optimal condition (i.e., sulfuric acid concentration exceed 100 g/L, temperature of 80 °C, pulp density of 10%, leaching time of 48 h), over 85% Zn was extracted into the leaching solution together with only about 10% Cu and Fe, according to the leaching experiment. Leaching slurry had good solid-liquid separation characteristics, and zinc can be further effectively recovered from the leaching solution. According to X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) analysis, chalcopyrite was the main mineralogical phase in the residues, which can be regarded as high quality copper concentrate for metallurgy. Accordingly, a new process for deep and efficient separation of Cu-Zn mixed ores has been proposed.

Selective recovery of valuable metals from nickel converter slag at elevated temperature with sulfuric acid solution

Abstract High pressure oxidative acid leaching (HPOXAL) was employed to extract valuable metals from nickel converter slag. Parameters such as sulfuric acid concentration, temperature, liquid/solid (L/S) ratio, leaching time, oxygen partial pressure and particle size were investigated to optimize the solubility of metal values and improve the solid–liquid separation characteristics of the leaching slurry. A highly selective leaching of valuable metals with extraction of >97% for cobalt and nickel, >95% for copper and 2 h. The residue containing hematite, silica and

Selective recovery of valuable metals from partial silicated sphalerite at elevated temperature with sulfuric acid solution

The purpose of this work was to study the feasibility at laboratory-scale of a hydrometallurgical process for the selective recovery of valuable metals from partial silicated sphalerite in an oxygen pressure acid leaching system. The factors influencing dissolution efficiency of the ore were investigated and optimized. Under optimum conditions (i.e., temperature of 433K, sulfuric acid concentration of 41.2g/L, leaching time of 2.5h, liquid/solid ratio of 6mL/g, and pressure of 1.6MPa) over 97% Zn was extracted into the leach liquor together with 0.3% SiO2 and 2.9% Pb. The leaching slurry had good solid–liquid separation characteristics, and the filtration rate could be as high as 716L/m2h. About 96% oxidation of sulfide sulfur to sulfate was achieved under these conditions. Analysis of the content of elemental sulfur in the leaching residues indicated that the fraction of sulfide sulfur determined as elemental sulfur was about 10% at 393K, and that it decreased with temperature down to 0.5% at 453K. Ultimate solid residues, which have been concentrated in silica and lead, can be oriented toward the lead smelter after alkali roasting-water washing pretreatment for metal recovery.

The solid–liquid separation characteristics of pure LiCl–KCl eutectic salt using different types of crucibles

Uranium deposits were recovered at the solid cathode of an electrorefining system, and deposited uranium dendrite normally contains about 30–40 wt% LiCl–KCl eutectic salts. Therefore, a separation of the eutectic salts from deposited uranium is essential for reusing these salts and uranium. A process such as distillation was employed for cathode processing due to the advantages of a minimal generation of secondary waste, a compact unit process, and simple and low-cost equipment. However, the realization of a wide evaporation area or high distillation temperature is limited by various factors such as the material or structure of a distiller. Also, the electrical energy flow from outside has a lot of consumption to maintain the high temperature. Hence, in this study, solid–liquid separation experiments are proposed to increase the throughput of the salt removal process by the separation of the liquid salt prior to the distillation of the LiCl–KCl eutectic salt. The solid–liquid separation of salt was carried out in a vertical type distiller. The behavior of the solid–liquid separation of pure eutectic salt was investigated as a function of temperature, pressure, sieve size, and crucible shape. From the experimental results using pure eutectic salts, the amount of salt separation was achieved at more than 94 wt%. The rate of solid–liquid separation of salt using 600 °C is higher than that of 500 °C under the same condition. The influence of a vacuum for solid–liquid separation can be disregarded, and the separation rate of a 100 mesh was higher than that of a 150 mesh. In addition, the rate of separation for salts using a porous crucible is higher than that in a non-porous crucible.

Metal sulphides from wastewater: Assessing the impact of supersaturation control strategies

Metal sulphide precipitation forms an important component of acid mine drainage remediation systems based on bacterial sulphate reduction. However, the precipitation reaction is inherently driven by very high levels of supersaturation with the generation of small particles with poor solid–liquid separation characteristics. In this study, the effect of strategies used to manage supersaturation was investigated during copper and zinc sulphide precipitation reactions. Initial batch studies showed the origin of sulphide (biological or chemical) had no significant effect on the efficiency of zinc sulphide precipitation. For copper, low metal removal efficiency was obtained at metal to sulphide molar ratios below 1.6 in the synthetic sulphide system. This was improved in the biogenic sulphide system, due to the presence of residual volatile fatty acids, but the presence or absence of particulate organic matter had no effect on recovery. Subsequent studies, conducted using synthetic sulphide solutions in a seeded fluidised bed reactor with multiple reagent feed points (2FP and 6FP) and different recirculation flow rates (300 and 120 mL min−1) showed efficient zinc sulphide precipitation, but limited (<10%) deposition on the seeds. Increasing the number of sulphide feed points (2–6) reduced precipitate loss as fines by approximately 10%. Zinc sulphide fines could be effectively recovered from suspension by settling under quiescent conditions. In the copper system, metal recovery was low (ca 40%) due to the formation of very small copper sulphide particles (mean particle size of ca 0.01 μm). Increasing the number of reagent feed points did not affect supersaturation to the extent of altering particle characteristics. The copper sulphide fines could not be recovered by settling, remaining in a stable colloidal suspension due to their highly charged surfaces (zeta potential −50 mV). The change in recirculation flow rate had a limited effect (ca 5% improvement) on process efficiency. The results show that the extremely high supersaturation prevalent during metal sulphide precipitation is difficult to control using conventional approaches and suggest that the seeded fluidised bed reactor is not suitable for this application.

Simultaneous removal of organic matter and nitrogen from milking parlor wastewater by a magnetic activated sludge (MAS) process

The magnetic activated sludge (MAS) process is a modification of the conventional activated sludge process to improve the solid–liquid separation characteristics. It was developed to reduce the production of excess sludge and the time required for the conventional activated sludge process. In this study, actual milking parlor wastewater was treated with a MAS process and no sludge was removed. The effectiveness of continuous aeration and intermittent aeration in removing organic matter and nitrogen were compared. Both processes were highly efficient at removing chemical oxygen demand (COD) (averaged 91% removal) and ammonium nitrogen (NH4-N) (averaged 99% removal). In marked contrast to the continuous aeration process, the 30-min aeration/90-min non-aeration cycle of the intermittent aeration process rapidly reduced the nitrate nitrogen (NO3-N) concentration to near-zero. This result indicates that NO3-N was almost completely denitrified via nitrite nitrogen (NO2-N) to nitrogen gas. Removal of organic material and nitrogen can be considered to have occurred simultaneously in the single tank of the MAS process.

The Effect of Freezing and Thawing Treatment on the Solid Liquid Separation Characteristics of Bulking Activated Sludge

下水または排水処理に一般に用いられている活性汚泥処理では曝気槽内の活性汚泥が非常に沈降しにくいバルキング状態になることがあるが, その場合最終沈殿池における固液分離が困難になるため下水または排水の処理を継続できなくなる. また, 一般の下水処理施設から出る余剰活性汚泥は非常に脱水しにくいことが知られているが, 我々はその固液分離特性が凍結融解処理によって顕著に改善されることを明らかにしてきた.本報においては, グルコースとペプトンを基質として馴致して得たバルキング汚泥と正常な固液分離特性を有する汚泥に凍結融解処理を施して固液分離特性に及ぼす影響を調べ, 下水処理場から採取した下水汚泥との比較も行った. その結果, 凍結融解処理を行うと全ての汚泥の沈降性は改善され, フロックも緻密になることがわかった. また, バルキング汚泥は他の汚泥に比べて濾過しにくいが, 凍結融解処理による濾過特性の改善の程度は他の汚泥と同じであることもわかった.

亜鉛ダストの再資源化技術 微粒子選別への磁選法の適用

Zinc dust generated from recycling process of steelmaking dust must be pretreated by sintering prior to the reuse of zinc as a smelting raw material. The present paper proposes a novel magnetic separation process with ultrasonic dispersion, which recovers zinc oxide with the average size of 1 micron from the zine dust with a low energy consumption and recycling cost. The proposed prosess significantly improved the recovery and grade of zinc concentrate (contained 64% zinc at 80% recovery) over the conventional magnetic separation, without influencing the solid-liquid separation characteristics of concentrates. The improvement in the recovery and grade was resulted from the dispersion of fine particle aggregates in the magnetic separation cell by the ultrasonic wave.

The Effect of the Freezing Column Diameter on Freezing and Thawing Treatment of Excess Activated Sludge.

The solid liquid separation characteristics of activated sludge are significantly improved by a freezing and thawing treatment. This improvement is much affected by the freezing rate when using the same freezing column. In this study, the effect of the freezing column diameter (inner diameter: 16-147 mm) on the freezing and thawing treatment is investigated. This parameter is important for scale up purposes. For inner diameters greater than 40 mm and at a constant freezing rate of 2 mm/h, changes in the freezing column inner diameter had a minimal impact on both the solid liquid separation characteristics and the decreasing ratio of the biological activity. Consequently, for the freezing columns with inner diameters of 40 mm and above, scale up of the freezing and thawing equipment can be undertaken with confidence.

Simultaneous removal of organic and nitrogen compounds in intermittently aerated activated sludge process using magnetic separation

Magnetic separation was introduced to an activated sludge process to improve the solid-liquid separation characteristics of the sludge. The process was operated with the intermittent aeration method and applied for the removal of organic matter and nitrogen in wastewater. The activated sludge supplemented with magnetite (Fe 3O 4) powder (magnetic sludge) exhibits a ferromagnetic property and deposited on the surface of magnetic disks due to magnetic force. The magnetic separation apparatus (composed of rotary magnetic disks and scrapers) separated treated water from the sludge suspension of 13–22 g VSS l −1 within 5 min. Compared with the sedimentational separation process, the magnetic separation technique showed better performance. Simultaneous removal of about 89% of TKN and about 92% of soluble COD Cr in influent was performed under loading rates of 0.92 g COD Cr l −1 d −1 and 0.10 g TKN l −1, respectively, with a non-aeration/aeration cycle of 40/20 min.

Particulates in hydrometallurgy: Part III. Dewatering behavior of flocculated laterite acid leach residues

Three polyacrylamide-based polymers of different chemical properties (polymer A, 34 pct anionic, 11×106 mol wt; polymer B, 7 pct anionic, 7.5×106 mol wt; polymer C, nonionic, 13.5×106 mol wt) were used to evaluate the flocculation behavior of laterite acid leach residues. The solid-liquid separation characteristics of the leach residues were investigated with the aid of settling rate, supernatant turbidity, and slurry filtrability measurements. The polymeric flocculants were found to be effective in improving the dewatering properties of the acid leach residues. Polymer effectiveness increased with increasing polymer dosage for all the polymers, but an optimum polymer dose was only found for polymer A (34 pct anionic, 11×106 mol wt) in the studied range of polymer addition. Similarly, the dewatering behavior was improved at higher polymer molecular weight. In addition, it was found that the flocculation performance was adversely affected by an increase in the degree of polymer hydrolysis which, in turn, increases the ratio of carboxylic to amide functional groups in the polymer chain. Polymer C (nonionic ∼0 pct hydrolysis, 13.5×106 mol wt) was found to be the most efficient flocculant in terms of all the performance criteria investigated. The preceding results were rationalized in terms of bridging flocculation, the ionization and molecular configuration of the polymers, hydrogen bonding, and the solid/aqueous interfacial charge.

Compression-Permeability Characteristics and Effect of Freezing and Thawing Process of Excess Activated Sludge.

The characteristics of compression and solid-liquid separation of excess activated sludge were investigated. Compression-permeability experiments were made under low solid compressive pressure (10 3 -10 5 Pa), and centrifugal settling experiments under 30-2000 Pa. In these experiments, we used excess activated sludge from a municipal wastewater treatment plant and sludge treated by a freezing and thawing process. An equation for inorganic sludge (1-e=E.p s β ) is proposed, where e and p s are the porosity and the solid compressive pressure, and E and β are empirical constants for each sludge. The equation can be applied to both experiments, if the average values of e and p s which were defined previously by the authors are used in the centrifugal settling experiment. Consequently, the compression characteristics over a wide range of p s can be estimated by a centrifugal settling experiment which is relatively simple. The relationship between local specific filtration resistance α and p s can be represented by a straight line which has a bending point at the pressure where e w is nearly equal to zero. The freezing and thawing treatment of excess activated sludge diminishes the specific filtration resistance of the sludge by more than one order over the whole experimental range of p s . This implies that the treatment improves the solid-liquid separation characteristics of excess activated sludge

Compression characteristics of excess activated sludges treated by freezing-and-thawing process.

Excess activated sludge is very difficult to be filtered, but its solid–liquid separation characteristics can be improved by a freezing-and-thawing process. In this study, centrifugal and the gravitational settling experiments were done by using unfrozen and frozen activated sludges.An equation for the average solid compressive pressure ((ps)av) in the sediment zone was derived, based on the general equation for the local compression characteristics of a solid–liquid mixture. Also, the relationship between (ps)av and the average porosity ((es)av) in the sediment zone (1 – (es)av) = E(ps)avβ; E and β = constants) was confirmed by centrifugal and the gravitational settling experiments.The order of magnitude of (e)av was unfrozen sample

Batch crystallization and solid-liquid separation of potassium sulphate

The physical form of potassium sulphate crystals produced in laboratory scale batch crystallizers by both cooling and by precipitation is studied in terms of its subsequent effect on solid-liquid separation characteristics. Control of operating conditions improves the crystal size distribution in both cases and considerably increases the permeability of the precipitates.