ESP Dust Research Articles

Selective recovery of scandium with acid solutions of magnesium sulphate from ESP dust generated by bauxite sintering plants

Among potential sources of scandium and other rare earth elements (REEs) there are semiproducts generated by the alumina industry. They include red mud and ESP dust generated by sintering plants. Most of the previous research studies focused on red mud leaching using a variety of strong acids. However, because of the need to neutralize the caustic alkali present in red mud, as well as to dissolve iron and other macrocomponents, the above process is associated with a high consumption of reagents. This paper examines the possibility to selectively recover REEs from ESP dust at high pH values in the presence of magnesium cations. It is shown that the prior water leaching of ESP dust helps achieve a double rise in the REE concentration and considerably lower the concentration of Na2O in the solid residue. For selective recovery of REEs, the authors used weak solutions (pH = 2÷5) of sulphuric acid with magnesium sulphate. The latter help to desorb REEs from the surface of minerals contained in the solid residue. Over 75% Sc was recovered through solid residue leaching conducted at the temperature of 80 oC, liquid-to-solid ratio of 10:1 and duration of 60 min at pH = 2. The recovery of iron and titanium did not exceed 1–5%. With all other conditions being equal, raising pH to 3.5 would lead to a drop in the scandium recovery to 63% while the recovery of iron and titanium would drop to 0.2%. It was also found that, as the result of sulphuric acid leaching, the calcium that is present in the initial ESP dust gets precipitated in the form of gypsum and a certain amount of REEs may get carried away. This research was carried out as part of Grant No. 22-29-01515 of the Russian Science Foundation; the concentration of rare earth elements in the solid residue was determined through inductively coupled plasma mass spectrometry, supported through an assignment of the Government of the Russian Federation under Grant No. 075-03-2021-051/5.

Strategies for arsenic pollution control from copper pyrometallurgy based on the study of arsenic sources, emission pathways and speciation characterization in copper flash smelting systems.

Arsenic in copper flash smelting (FS) systems not only affects the quality of products but also poses significant technological and environmental problems. Based on the assessment of arsenic mass partitioning in the FS system, arsenic elimination in off-gassing and tailings is 22%, and most of the arsenic output (69%) is recycled in the FS system. Circulating arsenic, especially arsenic in recycled dust and slag concentrate, is the key reason for high-arsenic-content feed. Dust-type recycled materials (RMs) contribute much more arsenic to the feed than slag-type RMs. Flash smelting furnace electrostatic precipitator (FSF ESP) dust contributes makese the largest contribution to arsenic among the dust-type RMs of mixed dust, especially trivalent arsenic, followed by FSF and flash converting furnace waste heat boiler (FCF WHB) dust, which contributes pentavalent arsenic. FCF WHB dust exhibits a relatively low arsenic content, consisting mainly of As(V)-O. Slag-type recycled materials contribute As(V)-O to the total feed, and As(III) originates from copper concentrates. Considering the arsenic contribution and environmental risk, reducing the recovery of FSF ESP dust can greatly decrease the arsenic grade of FSF feed and volatile As2O3. As one of the main arsenic sources in feed, FSF slag concentrate should be carefully disposed of if separated from feed materials because of its high arsenic-related environmental risk. In contrast, WHB dust and FCF slag are more suitable as RM due to their high copper content and low arsenic risk.

Effect of Iron-Bearing By-products on the Emission of SO2 and NOx in the Iron Ore Sintering Process

Iron-bearing by-products are rich in iron and carbon and are often reused in the iron ore sintering process. However, there are fewer studies on the effect of them on sintering flue gas pollutants. Four kinds of iron-bearing by-products were chosen to investigate the effect of them on the emission of SO2 and NOx and sinter quality through sinter-pot test. The results showed that all iron-bearing by-products promoted the emission of SO2, while steel slag tailings and mill scale inhibited the emission of NOx, and blast furnace dust and the sintering ESP dust promoted the emission of NOx. The main cause of blast furnace dust and the sintering ESP dust promoted the emission of SO2 and NOx was the residual unburned coke particles in them. The main cause of steel slag tailings and mill scale promoting the emission of SO2 and inhibiting the emission of NOx was the abundant iron oxides and calcium ferrite. In addition, the effect of them on sinter quality was slight. For reducing the emission of sintering flue gas pollutants, the addition ratio of blast furnace dust, steel slag tailings and mill scale should be controlled to be 1–3%, 3–4% and 2–5%, respectively. The sintering ESP dust from the 3rd electric field should not be added to raw materials, and the addition ratio of the dust from the 1st electric field and the 2nd electric field should be controlled to be 2–3%.

An evaluation of testing and modeling procedure for solids friction factor for fluidized dense-phase pneumatic conveying of fine powders

For the reliable design of a pneumatic conveying system, accurate estimation of solids friction factor through horizontal straight pipe is of paramount interest. Although the “straight pipe” method is fundamentally more appropriate, the “back calculation” approach provides several practical advantages for testing and modeling. However, earlier literature reports that “back calculation” approach suffers from 40 to 150% inaccuracy in prediction of total pipeline pressure drop in scale-up pipes, which had been discouraging for its use. In the present work, it has been argued that much of the criticism for the inaccuracy of back calculation method lies with the choice of its format of modeling solids friction factor. In this paper, “back calculation” method of modeling has been used by employing a “two layer” model format for solid friction factor for fly ash, ESP dust and cement. These models, when scaled up to predict the total pipeline pressure drop in larger and longer pipelines, have resulted in overall deviation from experimental data ranging from 3 to 35%, which is a significant improvement in prediction capability. The results prove that the selection of a better format of model for solids friction factor could significantly improve the reliability of “back calculation” method.

The Potential of Remedial Techniques for Hazard Reduction of Steel Process by Products: Impact on Steel Processing, Waste Management, the Environment and Risk to Human Health.

The negative impact from industrial pollution of the environment is still a global occurrence, and as a consequence legislation and subsequent regulation is becoming increasingly stringent in response, in particular, to minimising potential impact on human health. These changes have generated growing pressures for the steel industry to innovate to meet new regulations driving a change to the approach to waste management across the industrial landscape, with increasing focus on the principles of a circular economy. With a knowledge of the compositional profiles of process by-products, we have assessed chemical cleaning to improve environmental performance and minimise disruption to manufacturing processes, demonstrating re-use and recycling capacity. We show that with a knowledge of phase composition, we are able to apply stabilisation methods that can either utilise waste streams directly or allow manipulation, making them suitable for re-use and/or inert disposal. We studied blast furnace slags and Portland cement mixes (50%/50% and 30%/70%) with a variety of other plant wastes (electrostatic precipitator dusts (ESP), blast furnace (BF) sludge and basic oxygen furnace (BOF) sludge) which resulted in up to 90% immobilisation of hazardous constituents. The addition of organic additives i.e., citric acid can liberate or immobilise problematic constituents; in the case of K, both outcomes occurred depending on the waste type; ESP dust BF sludge and BOF fine sludge. Pb and Zn however were liberated with a 50–80% and 50–60% residue reduction respectively, which generates possibilities for alternative uses of materials to reduce environmental and human health impact.

Modeling solids friction factor for fluidized dense-phase pneumatic transport of powders using two layer flow theory

Fluidized dense-phase pneumatic conveying of powders is becoming increasingly popular in various industries, such as power, chemical, cement, refinery, alumina, pharmaceutical, limestone, to list a few, due to the reasons of reduced gas flows and power consumption, improved product quality control, reduced pipeline sizing and wear rate, increased workplace safety etc. An accurate estimation of total pipeline pressure drop is of paramount importance for the reliable design of a pneumatic conveying system. However, because of the highly concentrated and turbulent nature of the gas–solids mixture, fundamentally understanding the flow mechanism and accurately predicting the pressure drop as an important design parameter has only made limited progress so far. This paper results from an ongoing investigation into developing a validated modeling procedure for solids friction factor for the accurate prediction of pressure drop and optimal operating conditions for fluidized dense-phase pneumatic conveying systems. Under the present study, a two-layer based model has been developed by separately considering the solids friction contributions of the non-suspension (dense) bed of powders flowing along the bottom of pipe and the suspension (dilute-phase flow) of particles occurring on top of the non-suspension layer. Volumetric loading ratio and dimensionless velocity have been used to model the non-suspension dune flow layer. A solids impact and friction term and dimensionless velocity have been employed to model the dilute-phase flow due their established reliability. Models have been developed using the straight-pipe conveying data of two types of fly ash, cement and ESP dust (median particle diameter: 7 to 30μm; particle density: 2300 to 3637kg/m3; loose-poured bulk density: 610–1080kg/m3). The developed models for solids friction were validated for their scale-up accuracy by using them to predict the pressure drops in five larger and longer pipelines (69mm I.D.×168m long; 105mm I.D.×168m long; 69mm I.D.×554m long, 65mm I.D.×254m long and 80/100mm I.D.×407m long pipes) and by comparing the experimental versus predicted pneumatic conveying characteristics. The two-layer model provided improved accuracy compared to existing models indicating that the model is able to adequately address the dense- to dilute-phase transition criteria.

Analysis of Physical and Chemical Features of Sintering Dust and Study of Recycling Treatment

Several physical and chemical detection methods were used to study the basic properties of sintering dust collected from Baogang Steel Corporation. The result shows that the major constituents of the electrostatic precipitator dust (ESP dust) were KCl, NaCl, Fe2O3 and Fe3O4. Water leaching experiment on the sintering dust had shown that the KCl in the ESP dust could be separated and recovered by water leaching and fractional crystallization. Component analysis of leaching solution showed that the massive calcium sulfate in the leaching solution should be removed first in order to obtain the pure potassium salt. In order to provide theoretical guidance to inhibit the dissolution of calcium ions from the sintering dust, the water leaching experiment of ESP dust and the dissolution behavior of CaSO4 in the potassium chloride, sodium chloride, potassium sulfate and their mixed salt solution were studied. Result showed that, a lower liquid-solid ratio should be chosen in the leaching process to inhibit the dissolution of calcium sulfate dehydrate. Using sodium carbonate solution as a precipitating agent, the influences of the concentration of sodium carbonate solution, reaction temperature, stirring speed on the preparation of the spherical calcium carbonate were studied. Spherical calcium carbonate with good dispersing performance and grain size distribution in nanometer range of less than 10μm was obtained. The production technology of potassium sulfate by double decomposition was sutdied, the results showed that over 80% and 12.76% of the recovery rate of potassium sulfate and potassium chloride ammonium compound fertilizer could be obtained. Furthermore, a potassium recovery process with joint production of spherical calcium carbonate and potassium sulfate was designed. This process is technically viable and considerable in economic benefit.

Preparation of potassium salt with joint production of spherical calcium carbonate from sintering dust

Several physical and chemical detection methods were used to study the basic properties of sintering dust (ESP dust) collected from Baogang Steel Corporation. The result shows that the major constituents of the ESP dust are KCl, NaCl, Fe2O3 and Fe3O4. Water leaching experiment on the sintering dust shows that KCl in the ESP dust can be separated and recovered by water leaching and fractional crystallization. Component analysis of leaching solution indicates that the massive calcium sulfate in the leaching solution should be removed first in order to obtain the pure potassium salt. In order to provide theoretical guidance to inhibit the dissolution of calcium ions from the sintering dust, the water leaching experiment of ESP dust and the dissolution behavior of CaSO4 in the potassium chloride, sodium chloride, potassium sulfate and their mixed salt solution were studied. It is found that, a lower liquid–solid ratio should be chosen in the leaching process to inhibit the dissolution of calcium sulfate dehydrate. Using sodium carbonate solution as a precipitating agent, the influences of the concentration of sodium carbonate solution, reaction temperature, stirring speed and equilibrium time on the preparation of the spherical calcium carbonate were studied. Spherical calcium carbonate with good dispersing performance and grain size distribution in nanometer range of less than 10 μm was obtained. Furthermore, a potassium recovery process with joint production of spherical calcium carbonate was designed. This process is technically viable and considerable in economic benefit.

On improving solid friction factor modeling for fluidized dense-phase pneumatic conveying systems

This paper presents results from an ongoing investigation into the modeling of solid friction factor for fluidized dense-phase pneumatic transport of powders. In spite of having the potential of being an energy economic and a better maintenance free mode of pneumatic transport, reliable design of fluidized dense-phase pneumatic conveying systems is still a difficult task due to the highly turbulent and complex nature of the flow of fine powders under high concentrations, where is it difficult to model particle–wall–air interactions. Several popular/applicable models (developed by other researchers, including one of the co-author of this paper) were evaluated to predict the total pipeline pressure loss for the dense-phase pneumatic conveying of fly ash (median particle diameter: 30μm; particle density: 2300kg/m3; loose-poured bulk density: 700kg/m3) and ESP dust (median particle diameter: 7 μm; particle density: 3637kg/m3, loose-poured bulk density: 610kg/m3) under different diameter and length scale-up conditions (viz. 69mm I.D.×168m; 105mm I.D.×168m and 69mm I.D.×554m pipes). These models are based on solids loading ratio and Froude number). A comparison between the predicted pneumatic conveying characteristics (PCC) and the experimental results showed that the models resulted in significant inaccuracy, especially under scale-up conditions of a new modeling technique has been developed using air velocity and a volumetric loading ratio term by replacing solid loading ratio and Froude number. The volumetric loading ratio term intends to address the product volume occupancy inside the pipeline, which is believed to be a better representation of flow conditions compared to mass ratio. The derived models were examined for scale-up accuracy by predicting pressure drop for different diameter/lengths of pipelines. It is found that the models have generally provided improved predictions in the dense-phase region. Whereas the existing models predicted with relative errors varying between 10 and 127% (depending on product and pipeline conditions), the new developed model resulted in predictions within 24% accuracy for a wide range of scale-up conditions, which provides better reliability and a narrower range of predictions, more suitable for industrial scale up requirements. Future work would require a more fundamental approach to understand the solid friction phenomenon for further accurate modeling.

Water leaching kinetics and recovery of potassium salt from sintering dust

Surface morphology and inner structure of the dust were observed by ICP-AES, SEM-EDS and XRD to examine the strengthening measures of leaching potassium salt from the sintering dust by water. The results showed that the main component of the sintering dust was iron–oxygen compound, with KCl adsorbed on its surface. Leaching experiments showed that the KCl in the ESP dust could be separated and recovered by water leaching and fractional crystallization. The yield of K–Na vaporized crystalline salt was 18.56%, in which the mass fractions of KCl, NaCl, CaSO4 and K2SO4 were about 61.21%, 13.40%, 14.62% and 10.86%, respectively. The leaching kinetics of potassium salt from the sintering dust fits the external diffusion model well. The leaching speed and the leaching rate of the potassium salt can be increased by increasing the leaching temperature, strengthening the stirring speed and increasing the liquid–solid ratio.

On Improving Scale-Up Procedures for Dense-Phase Pneumatic Conveying of Powders

This article presents results of an ongoing effort toward improving the modeling and scale-up procedures for the dense-phase pneumatic conveying of fine powders through pipes. Two new approaches are employed in this study. One approach, derived by modifying an existing reliable dilute-phase model to make it suitable for the dense-phase, has resulted in relatively stable predictions for diameter and length scale-up for two types of fly ash, ESP dust, pulverized brown coal and fly ash/cement mixture. Although some over-predictions still remain for the cases of diameter scale-up, there seems to be a substantial relative improvement in the overall accuracy of predictions (compared to the existing design methods). Another method has been derived using the concept of “two-layer” slurry flow modeling (suspension flow occurring on top of a non-suspension moving layer), and this has also resulted in similar improvements. Although the “two-layer” technique is believed to be more representative of the actual flow conditions under dense-phase conveying, the simpler “modified” method appears to be adequate for practical design purposes.

Characterisation of ESP Dust Sample from Sinter Plant

Characterisation of ESP Dust Sample from Sinter Plant

Separation and Recovery of Potassium Chloride from Sintering Dust of Ironmaking Works

Sintering plant in iron and steel making company generates very fine metal-containing dusts which can present major environmental problems. This paper describes experimental work on a relatively simple and inexpensive process for recovering the potassium chloride and upgrading the iron level of dust from a Chinese plant, to produce saleable potassium chloride product and environmentally safe waste products for reuse. The dust contained about 10–20% potassium as potassium chloride, 20% iron as iron oxides, plus small quantities of lead, copper, cadmium, zinc and other materials. Individual particles of the dust were commonly aggregates of various shapes. Multi-stage countercurrent leaching was taken to completely remove potassium chloride in the ESP dust, but leave iron in the leach residual. With the help of sodium sulfide precipitation, the leached heavy metals were removed from the leaching solutions and a mixture solution which can be perceived as system KCl–NaCl–CaCl2–H2O was left. Then potassium chloride in the system can be separated and recovered by fractional crystallization. At last the mother liquor was returned to the leaching process as leaching agent together with new tap water. This proposed flow sheet was proved feasible through construction of the demonstration unit in the lab, and KCl product with a purity of 96.5% was obtained.

Discovery of Potassium Chloride in the Sintering Dust by Chemical and Physical Characterization

Sintering plant dust arrested by electrostatic precipitator (ESP dust) in an integrated iron and steel company is perceived as a precious secondary material to steelmaking process, due to the presence of important elements to the industry such as, Fe and C with an attractive concentration. However, some hazardous elements such as, K, Na, Zn, Pb, seriously destroying normal working of the blast furnace, are enriched meanwhile. Therefore, it becomes very important to know how to separate these elements from Fe and C before reusing the dust. The aim of this work is to carry out a chemical, physical, structural and morphological characterization of the sintering dust. The dust was subjected to granulometry analysis, chemical analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy via SEM (EDS), X-ray mapping analysis via SEM and X-ray diffraction. With the help of these analysis ways and some comparison made between characterization of the dust before and after water leaching, an encouraging conclusion was drawn: KCl was identified in the sintering dust with a content percentage up to 30%. Considering serious lack of potassium fertilizer in China, it is necessary to recover KCl from the sintering dust. In addition, endanger of K to the steelmaking process is restricted at the same time.

Electrodialysis Field Test for Selective Chloride Removal from the Chemical Recovery Cycle of a Kraft Pulp Mill

Chloride accumulation is a serious issue in the kraft pulping process. Chloride can be selectively removed from dissolved electrostatic precipitator dust (ESP dust) in the kraft chemical recovery cycle by electrodialysis with monovalent-selective anion-exchange membranes. In a pilot-scale field test, this process was investigated (total run time, 750 h). The test was performed at about 3.5% of full scale. The process showed outstanding performance and no significant membrane fouling. In feed-and-bleed operation, chloride removal levels of 94% and 61% were tested. The energy consumption for electrodialysis is low (120 kWh per metric ton of chloride removed at a 63% chloride removal level). The process performed very well even with no feed pretreatment, polarity reversal, or membrane cleaning.

Processing of spodumene-modified mullite ceramics

The use of β-spodumene (Li2O·Al2O3·4SiO2) has been investigated as a liquid-phase sintering aid for the densification of mullite processed from fumed silica and ESP (alumina) dust. XRD, DTA, SEM and Vickers indentation were used to characterize the effect of spodumene on the phase relations, sintering behaviour, microstructure and mechanical properties of mullite. The results show that the presence of spodumene significantly reduces the porosity, improves the sintering behaviour and enhances the formation of mullite at 1550 °C. Spodumene-modified mullite ceramics also have better physical and mechanical properties.

Statistical analysis of heavy metal data from municipal waste incineration residues

Heavy Metal data from a measurement program at a municipal incinerator in Vienna, Austria are analysed. The experimental design had a nested structure, and analysis of variance is used to break down the total variability into several components; (1) variability between mean hourly concentrations, (2) variability between mean sample concentrations within intervals of an hour and (3) variability due to "measurement" errors. Results of a pre-experiment show, that if grab samples are taken, within hour variation is dominant. The results of analysis of variance were used to calculate an optimal number of samples, which ensure a predetermined accuracy for the mean concentrations. In two main measuring periods with different incinerated waste types, slag and fly ash (ESP dust and boiler ash) data are produced and analysed. For both slag and fly ash, significant differences in measures of location and dispersion between the data sets of the main experiment are found. This proves, that differences in the chemical set up of waste can be detected via incineration residues.

Positive effects of cement kiln exhausts on legume crops under simulation study

Soil application of cement kiln exhausts (electrostatic precipitator dust) at both lower and higher concentrations did not inhibit growth, nodule formation, and productivity inCajanus cajan, vigna radiata, andVigna mungo. In fact, growth was promoted, possibly because of the dust containing most of the elements, such as N, Ca, Fe, Mg, Mn, K, Zn, P, S, and Cu, which are needed for plant growth and root nodulation. Foliar application of the dust did not affect chlorophylls and carotenoids. The rate of photosynthesis as measured by CO2 uptake and stomatal diffusive resistance of all legumes were not affected. There was a biomagnification of Mg and K in leaves and seeds. Addition of the ESP dust did not affect either the soil or nodule rhizobial population. It is evident that the dust did not act as a phytotoxicant but as an elixir of plant life.

Simultaneous sampling of PCDD/PCDF inside the combustion chamber and on four boiler levels of a waste incineration plant

At a MSWI (municipal solid waste incinerator) plant PCDD/PCDF samples (gasphase and particulates) were taken simultaneously be a shock-freezing method in the incinerator combustion chamber at approx. 800°C and in four sampling sections in the boiler at about 490°C, 370°C, 330°C and 270°C. In this way PCDD/PCDF-formation in the flow through the boiler was determined. Two data sets were evaluated. A considerable PCDD/PCDF-formation had occurred already at boiler temperatures of about 490°C; the highest concentration, however, was found at the end of the boiler at about 300°C. The accompanying measuring program of plant parameters made the calculation of the PCDD/PCDF mass flows possible, which allowed the inclusion of the PCDD/PCDF-content in the ESP dust in the mass flow calculations.