The Effect of Flocculants and Surfactants on the Filtration Dewatering of Iron Ore Fines

Abstract

The filtration and separation characteristics of iron ore fines have been investigated. The experimental work included: characterization, evaluation of suitable flocculants to enhance settling and dewatering rate, determination of optimum dosages of flocculants, and influence of surfactants on nitration dewatering of both flocculated and unflocculated iron ore fines by vacuum filtration. The results showed that 1) the settling rate can be enhanced many-fold (from 2.52 to 90 m/h) by a suitable flocculant, 2) the residual filter cake moisture content can be reduced from 18.2% without reagents to 12.6% with suitable surfactant dewatering aids while the filtration rate can be enhanced from 4.8 to 97.2 L/h with suitable dewatering filter aids, and 3) the specific cake resistance to filtration can be brought down from 8.6 × 10⁹ to 1.0 × 10⁹ m/kg by using a surfactant sodium petroleum sulfonate at a concentration of 1.47 × 10^?3 kg/t. The economics of using flocculant filter aids and surfactant dewatering aids before thermal drying is described and discussed.     

Experimental Study on Thermal Hydrolysis and Dewatering Characteristics of Mechanically Dewatered Sewage Sludge

After mechanical dewatering, sewage sludge has a moisture content of around 80 wt% and further disposal is required. A new sewage sludge semi-drying (dewatering) process is proposed and verified. It combines thermal hydrolysis and subsequent mechanical dewatering, with less energy consumption than traditional thermal drying. Sludge treated using this new process satisfies further disposal requirements (e.g., landfill or autothermal incineration). In the present study, a high-pressure test reactor was used to study the thermal hydrolysis of dewatered sludge. Thermally hydrolyzed sludge was subsequently dewatered by centrifugal sedimentation or by pressure filtration. The amount of organic compounds returning to the water phase was also measured. According to the results from centrifugal settling tests, the optimal thermal hydrolysis treatment temperature was 180°C. The moisture content then dropped to 1.44 kg/kg dry solids (DS; 59 wt%) after dewatering under relative centrifugal force of 9,000 × g from 5.67 kg/kg DS (85 wt%). Pressure filtration further reduced the moisture content of filter cakes to only 0.5 kg/kg DS (33 wt%, hydrolysis temperature 180°C). After thermal hydrolysis, the heating value of sludge (moisture-free basis) was about 80% that of the untreated sludge.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

A Study for Development of Real-Scale Thermal Filter Press Dewatering (TFPD)

Real-scale thermal filter press dewatering equipment (plate size: 630 mm × 630 mm) was installed and operated at a waterworks for one year in an attempt to achieve sludge reduction. During the period, the dewaterability was evaluated according to the seasonal sludge properties in order to compare the dewaterability of thermal dewatering and mechanical dewatering, as well as to determine the economics of thermal dewatering. According to the results, the winter season sludge showed a 36% decrease in water content and a two-thirds reduction in dewatering velocity compared to the summertime sludge. In addition, the dewatered cakes of the thermal filter press dewatering equipment showed a lower specific cake resistance and water content in the dewatered cakes than the mechanical filter press dewatering equipment, indicating superior dewaterability. This was attributed to the easier removal of the filtrate remaining in the capillary tubes due to thermal dewatering. The energy consumption for thermal dewatering was 300 kJ/dry solids (DS) kg. A comparison of the sludge dryers indicated that it is possible to produce dewatered cakes that consume less energy and can be recycled. According to the performance evaluation results, the real-scale thermal filter press dewatering equipment had high adaptability to the changes in seasonal sludge, showing excellent dewaterability compared to the mechanical filter press dewatering equipment, and was economical due to the lower energy consumption.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Statistical evaluation of hyperbaric filtration for fine coal dewatering

A statistical design of parametric study of pressure filtration for fine coal dewatering is presented. The effects of five major parameters of the dewatering, i.e. applied pressure, filtration time, cake thickness, solids concentration and slurry pH, on cake moisture reduction and air consumption were investigated. The study was conducted starting with two level factorial experiments to identify the most significant parameters, and concluding with response surface methodologies to establish an optimum operating condition for the dewatering of fine coal. It was observed that applied pressure, cake thickness and filtration time were identified to be the key operating variables for reduction of filter cake moisture as well as air consumption. With the key parameters, an optimum condition for the dewatering was determined to be an applied pressure of 93 psi with a cake thickness of 2.5 cm and a filtration time of 4.8 minutes for the laboratory filtration system. At these optimum conditions the filter cake containing about 22 percent moisture by weight and consuming air by 4.1 m³/(m²·min·kg) on dry solid basis was obtained.     

An Integrated Process of Olive Mill Wastewater Treatment

Abstract

Olive mill wastewater (OMWW) is considered as a challenge for environmental scientists. It is characterized by high values of total organics expressed by chemical oxygen demand (COD), biological oxygen demand (BOD₅), and phenols. In this paper, an integrated process of OMWW treatment, which includes lime precipitation, filtration using a novel technology of a membrane filter press (a pilot scale) and a post‐treatment using activated carbon adsorption for the filtrate, was studied. Lime precipitation has removed ～71% of phenols, ～39% of COD, and ～88% of BOD₅ with a rise in the total suspended solids (TSS) from 31 kg/m³ (before precipitation) to 69 kg/m³ (after precipitation).

The filtration and dewatering operation cycle is approximately 125–150 min. Filtration was examined at different feed pressure (3–5 bar), different slurry concentrations (23–69 kg/m³, dry weight), and filter aid pre‐coat with different additions of diatomite body feed. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite pre‐coating and slurry concentration increase. However, a further decrease in α values was obtained using diatomite body feed. Cake dewatering, via membrane squeezing, was applied using hot water (65°C) and cake moisture was dropped from ～64% before squeezing to 35% after squeezing. Twenty minutes were found enough for that stage to be accomplished. With vacuum application, for 30 min, over the hot cakes, cake moisture decreased to ～20% for cakes with an average thickness of 1 cm. The produced cakes lose more moisture by storing in open air (on the shelf), reaching an equilibrium value of 9% in 2–3 days. Calorific value of produced cake is 15.71 MJ/kg, suggesting strongly its use as an energy source. Activated carbon was used as an efficient sorbent for removing the remaining phenols and total organics from the filtrate as a post‐treatment showing promising results. Maximum removal of phenols and total organics, by lime precipitation and filtrate post‐treatment using activated carbon adsorption, reached ～99.7% and ～80%, respectively.

A process flowsheet and preliminary cost estimates are presented and compared with other processes. The thermal energy produced by the burning of the produced cakes would be enough for the thermal needs of both the olive mill plant and the proposed treatment process.     

Effect of Hydrodynamics During Crystallization on Mechanical Dewatering of Salicylic Acid

Mechanical cake dewatering is always desired to reduce the load on thermal dewatering (drying). Any change in the upstream process such as crystallization can have a significant influence on the filtration as well as cake dewatering characteristics. The present study deals with the effect of hydrodynamics (mixing intensity) during salicylic acid crystallization on the air dewatering characteristics in the subsequent pressure filtration. The mixing conditions during crystallization were varied by using three different types of agitators (anchor impeller [AI], curved blade turbine [CBT], and bar turbine [BT]) and by varying the speed of agitation. The effect of operating pressure and dewatering time on the final moisture content of the cake was also studied.

The crystal properties (crystal size and size distribution) were found to vary with the mixing intensity, which further influenced the cake dewatering kinetics as well as the residual moisture content. An AI, which is a laminar flow impeller, produced crystals with a wide size distribution and higher mean particle size, which resulted in cake with high porosity and hence higher moisture content. The high porosity (as well as high cake permeability) caused early air breakthrough, which resulted in ineffective dewatering of cake. Therefore, in this case the residual moisture in cake was found to be higher (27%) even at higher dewatering pressure (1.5 bar gauge) and longer dewatering time (90 s). A BT creates high turbulence during mixing and produced crystals with a relatively narrow size distribution and lower mean particle size, which provided low-porosity cakes. Such cakes could be efficiently dewatered and the final cake moisture content was found to decrease to about 15%, a significant improvement in the filterability of the cake. The dewatering data were modeled according to the correlation between irreducible cake saturation and capillary number for predicting the cake dewatering characteristics (residual moisture as well as dewatering kinetics) and the results were compared with the experimental data.     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used.

The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

Empirical Modelling of Cake Washing in a Pressure Filter

The focus of this article is on empirical modelling of filter cake washing. The filtration experiments introduced in this paper were conducted by using a pilot-scale (0.1 m²) filter press according to the basic principles of factorial designs. Five different variables of the filtration, pressing, cake washing, and air drying stages were considered in the tests and the examined product characteristics were the overall capacity of the filter and the purity of the cake. The results obtained from the tests were used for creating different kinds of regression models for explaining the influence of the studied variables on the success of the cake washing process. The goal of the modelling strategy for the cake washing was to determine the simplest empirical models and compare these with theoretical equations complemented with linear terms. It was found that the empirical equation could model the results more accurately than the theory-based equations could.     

热压过滤完善选煤工艺

论述了热压过滤干燥脱水机具有过滤与干燥的双重作用、脱水效率高等特点;分析了干燥压滤机内脱水峰面的形成和移动过程,以及物料中液体饱和度与时间的关系;介绍了热压过滤干燥工艺系统与装备,并通过应用实例说明其完善选煤工艺的意义。     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE*

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.

     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Tannery Waste Treatment: Leaching,Filtration and Cake Dewatering Using a Membrane Filter Press (a Pilot Plant Study)

Abstract

In Alcanena (Portugal) the waste water treatment plant (WWTP) receives tannery waste, after a pretreatment for sulphides and the tanning exhaust baths have been sent to a recovery unit and the municipal waste water from Alcanena residential area. Physical, chemical, and biological treatment processes are involved, and the end products are sludge of ～71% moisture containing mainly organic matter, sulfides, iron, chromium, and other metals. The sludge is dumped, after stabilization, in a specially designed hazardous waste landfill.

In this study, tannery mixed sludge (from chemical and biological treatments) was leached and filtered. Leaching was carried out using sulfuric acid (pH 0.5) to release residual sulfides and metals from the slurry. Hydrogen sulfide (H₂S) was flushed out into an oxidation trap (hypochlorite/alkaline tank) in which H₂S transforms to soluble sulfate. The acidified sludge was fed into a membrane filter press where it was filtered, acid‐washed, water–washed, membrane‐squeezed, and vacuum‐dried reaching lower moisture levels (20–30%). The process cycle is approximately 101–137 min in our experiments; however, from this work, a cycle of 90 min to produce cakes with 0.9 cm thickness in the industrial scale through cutting some operational time, reaching final moisture of ～20% at the end of the dewatering cycle, can be estimated. Filtration was carried out at different feed pressure (3–5 bar) with and without diatomite precoating. The effect of different amounts of diatomite body‐feed was studied. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite precoating and the increased amounts of diatomite body feed. Cake washing was accomplished using 0.05 M H₂SO₄ (acid washing), to remove residual metals, followed by water washing, to remove cake acidity. Cake dewatering via membrane squeezing was applied using hot water (65°C), and cake moisture was dropped from ～71% before squeezing to 42% after squeezing. With vacuum application over the hot cakes, for 30 min, cake moisture decreased to ～20% for cakes with an average thickness of 0.9 cm. Cake chemical analysis showed chromium levels lower than 1000 mg/kg (the maximum Cr concentration allowed by the Portuguese legislation in a solid residue for use in agricultural soil). In addition, produced cake (without diatomite body feed) has a calorific value of 11,000 kJ/kg and accordingly it can be used as a source of energy.     

Scale-up of steam pressure filtration

The characteristic of steam pressure filtration is the distinctive and even dewatering front. First, the interest has been focused on the main dewatering mechanism of steam pressure filtration. The question was whether the even and sharply distinctive dewatering front remains stable when the filtration face is scaled up by the factor 50. The experimental studies were carried through on a 3.75 m² disc filter which was modified for steam pressure filtration. A temperature sensor was installed in the rotating disc of the filter. The temperature at the filter cloth, opposite to the steam atmosphere is measured. The steam break through which determines the end of the mechanical displacement of the filtrate can be detected. The duration until the steam breaks through the filter cake in pilot scale is compared to the duration measured in lab scale. A simple calculation is presented which computes approximately the steam break through. The calculated steam breakthrough is also compared to the experimental data. The degree of moisture reached using the pilot scale steam filter is compared to conventional pressure filtration on the same pilot filter and data measured in lab scale.     

Density difference in pressure-filtrated wet cakes produced from spontaneous gelling slurries

Pressure filtration is a key process in ceramic forming; however, the influences of density difference in different parts of a pressure-filtrated wet cake on subsequent drying and sintering have not yet been explored. In the present work, alumina slurries dispersed by copolymers of isobutylene and maleic anhydride (PIBM) and ammonium salt of polyacrylic acid (PAANH₄) were pressure filtrated to examine the impacts of density difference in the as-prepared wet cakes. In comparison to the wet cake produced from PAANH₄, the wet cake with PIBM had much higher bulk density and smaller density difference between its upper and bottom parts (height of ~23 mm). Furthermore, in order to reveal the differences between these two wet cakes, the nature of agglomerates in their slurries was investigated. The slurry with PIBM contained agglomerates with a wider size distribution, bigger average size, and higher sphericity, producing a wet cake with a higher particle packing density and more homogeneous packing structure after pressure filtration. Hence, almost no deformation occurred in a large wet cake (280 mm × 130 mm × 20 mm) with PIBM, whereas that with PAANH₄ experienced a severe deformation after sintering.     

褐煤干燥水分回收利用及其研究进展

褐煤干燥提质过程中的水资源化回收利用工艺技术可以提高煤阶并回收宝贵的水资源,降低干燥提质单元能耗。本文从介绍褐煤中水的存在形态出发,围绕烟气直接干燥、蒸汽流化床干燥、微波干燥、机械热压脱水干燥等工艺综述了近年来干燥水回收利用的研究现状和最新进展,讨论分析了褐煤干燥与水回收利用工艺的选择原则。在回收褐煤中丰富的水资源时,除了单纯考虑回收褐煤中的水资源,还应权衡褐煤干燥工艺、干燥温度和干燥介质、干燥水蒸气的余热利用方式以及干燥工艺上下游间的衔接等因素。基于目前褐煤资源的主要用途,将干燥尾气采用换热技术回收低温余热和干燥冷凝水直接净化处理后的二次回用技术将是以后的重要研究和应用方向。     

Filtration and Drying Study of Phosphatidylinositol Fraction from De-Oiled Soy Lecithin

Separation and purification of phosphatidylcholine (PC) and phosphatidylinositol (PI) fractions to their utmost purity is still a challenging task industrially due to the molecular and structural complexity of lecithin molecules. The present study deals with the filtration of the PI-rich fraction followed by drying of the cake for its further purification and value addition. Filtration of the PI-rich fraction was carried out under constant pressure conditions followed by the drying of the cake in a vacuum tray dryer. The average specific cake resistance (α_av) as a function of operating pressure was studied and it showed little variation with respect to the applied pressure differential. The initial solvent content in the cake after filtration was found to be in the vicinity of 1 kg solvent/kg dry solid, which was then subsequently reduced in the drying stage to 0.04 kg solvent/kg dry solid. The drying kinetics of the cake was studied at different drying temperatures in a vacuum tray dryer operated under varying degree of vacuum. The drying rate curve showed a prominent falling rate period with the effective solvent diffusivity in the range of 5.4 × 10^?10 m²s^?1 to 1.42 × 10^?9 m²s^?1within the temperature range of 40–60°C. Critical analysis of the dried PI fraction was carried out in terms of phosphatidylinositol content and color. The drying data were analyzed using various models and Das et al.'s model, the modified Henderson and Pabis model, and the Page model were found to provide the best fit sin terms of root mean square error (RMSE), chi square, and correlation coefficient (R ²).     

Flow Resistance in Filter Cakes Due to Air

Abstract

The objective of this work is to show that air bubbles can adversely effect the performance of pressure filtrations. The effect of air on liquid flow resistance is measured in a well-characterized filter cake of Lucite particles. Air is introduced into the cake by allowing air bubbles to become entrained with the particles in the slurry at the start of filtration. Filtration with entrained air bubbles is compared to filtration without air bubbles. Experimental measurements show a significant increase in flow resistance due to the presence of air in a pressurized cake filtration. The presence of air bubbles in the filter cake can result in misinterpretation of experimental data. This in turn can increase operating and experimental testing costs and complicate efforts to predict filtration performance.