Preparation of activated carbons from heavy-oil fly ashes

The use of heavy oil fly ash with high ash content (45 wt.%) as a precursor for the preparation of activated carbons has been investigated. The raw fly ash and the fly ash with lower ash content, obtained by a HCl/HF washing treatment, have been pyrolyzed at 900 degrees C and then activated with CO(2) in the temperature range of 800-900 degrees C for different times. The activated carbons have been characterised as regards the surface area and the pore volume. The evolution of the porosity has been related to the burn-off degree.     

Synthesis of zeolite from waste fly ash for adsorption of CO2

Zeolitic sorbents for CO₂ adsorption were prepared from waste coal fly ash (FA) through hydrothermal treatment at various ratios of NaOH/FA and NaAlO₂/FA, including an initial alkali fusion step. The fusion step decomposed the fly ash into very small amorphous particulate zeolite forms. The fly ash was converted to Na-P1 type with a NaOH/FA ratio of 0.5 and Na-A type with a NaAlO₂/FA ratio of 0.53. The product properties were affected by the reaction temperature: Na-P1 and Na-A types were formed at 100°C. Temperatures above 140°C led to the formation of more sodalite because of the redissolving and recrystallization of zeolite crystals. Alkali metal and alkaline earth metal cations were impregnated in the synthesized Na-P1 and Na-A zeolite through an ion-exchange method. The completed zeolitic sorbents were applied to the adsorption of low-level CO₂. As a result of the experiments, calcium ions were found to be the best for CO₂ adsorption owing to their electrostatic behavior and acid-base interaction.     

碱激发粉煤灰对Cs~+的吸附行为

将粉煤灰进行碱激发改性,运用XRD和SEM技术对碱激发粉煤灰进行了表征,通过静态平衡吸附实验研究了碱激发粉煤灰对Cs+的吸附动力学和热力学特性,并对吸附前后的碱激发粉煤灰进行了FTIR分析。表征结果显示,碱激发处理后,粉煤灰的晶相发生了改变,且粉煤灰表面密实的硬壳层被破坏。实验结果表明:在初始Cs+质量浓度为200 mg/L、吸附温度为25℃、溶液pH为10、碱激发粉煤灰投加量为12.0 g/L的条件下,碱激发粉煤灰对Cs+的平衡吸附率可达80%以上,其吸附能力比碱激发前提高了3倍以上;吸附过程可用准二阶动力学方程来描述,并较好地符合Langmuir等温吸附模型;碱激发粉煤灰对Cs+的吸附是吸热过程,且能自发进行;该过程以物理吸附为主,并伴随化学吸附。     

Coal fly ash based carbons for SO2 removal from flue gases

Two different coal fly ashes coming from the burning of two coals of different rank have been used as a precursor for the preparation of steam activated carbons. The performance of these activated carbons in the SO₂ removal was evaluated at flue gas conditions (100 °C, 1000 ppmv SO₂, 5% O₂, 6% H₂O). Different techniques were used to determine the physical and chemical characteristics of the samples in order to explain the differences found in their behaviour. A superior SO₂ removal capacity was shown by the activated carbon obtained using the fly ash coming from a subbituminous–lignite blend. Experimental results indicated that the presence of higher amount of certain metallic oxides (Ca, Fe) in the carbon-rich fraction of this fly ash probably has promoted a deeper gasification in the activation with steam. A more suitable surface chemistry and textural properties have been obtained in this case which explains the higher efficiency shown by this sample in the SO₂ removal.     

Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

Sorbents synthesized from various types of ash (coal fly ash, coal bottom ash, oil palm ash, and incinerator ash) for flue gas desulfurization were investigated. The sorbents were prepared by mixing the ashes with calcium oxide and calcium sulfate using the water hydration method. The effects of various sorbent preparation variables, such as the hydration period, the ratio of calcium oxide to ash, and the amount of calcium sulfate, on the Brunauer-Emmett-Teller (BET)-specific surface area of the resulting sorbent were studied using a two-level full factorial design. The surface area of the sorbents obtained range from 15.4 to 122.1m²/g. Regression models were developed to correlate the significant variables to the surface area of the sorbents. An analysis of variance (ANOVA) showed that the model was significant at a confidence level of 95%. It was found that apart from all the individual variables studied, interactions between variables also exerted a significant influence on the surface area of the sorbent. From the activity test results, it was found that sorbents prepared from coal fly ash and oil palm ash have the highest SO₂ absorption capacity. Scanning electron microscope (SEM) analysis showed that the sorbent was composed of a compound with a high structural porosity, while an X-ray diffraction spectrum showed that calcium aluminum silicate hydrate compounds are the main products of the hydration reaction.     

Textural and surface chemical characteristics of activated carbons prepared from cattle manure compost

Two activated carbons (ACs) prepared from cattle manure compost (CMC) by ZnCl(2) activation were selected and out-gassed in a helium flow at various temperatures for 2h. The pore structure and surface chemical properties of the two selected ACs and their out-gassing treated ACs were characterized using N(2) adsorption-desorption, elements analysis, SEM and Boehm titration. A basic dye, methylene blue (MB), was chosen as an adsorbate to investigate the adsorption capacity for organic contaminant onto the activated carbons. It was found that the out-gassing treatment at 400 degrees C had little effect on the textural characteristics of the carbons but significantly changed the surface chemical properties such as surface functional groups concentration, pH and pH(PZC). The CMC-based activated carbons exhibited excellent performance for MB adsorption due to their high surface area, large mesopore volume and high nitrogen content. The kinetics of MB adsorption onto the activated carbons followed a pseudo-second-order equation, and the equilibrium data agreed well with the Langmuir model under the experimental conditions. The highest adsorption rate constant of k(ad) and the largest adsorption capacity of q(m) were found be 1.44x10(-4)g/mgmin and 519mg/g, respectively. The results suggested that the CMC-based activated carbons were effective adsorbents for the removal of methylene blue from aqueous solution.     

粉煤灰基吸附剂对模拟废水中Cd2+的吸附性能

以粉煤灰为原料、Na2CO3为助熔剂,采用盐熔融—水浴结晶法制备粉煤灰基吸附剂。探讨了吸附剂的最佳制备条件及其对模拟废水中Cd2+的最佳吸附条件、吸附动力学和吸附机理。实验结果表明:制备吸附剂的最佳工艺条件为m(粉煤灰)∶m(Na2CO3)为1∶2,焙烧温度为450℃;采用最佳制备工艺条件下制备的吸附剂(记作2-450℃-FA吸附剂),在初始Cd2+质量浓度为300 mg/L、初始溶液pH为7.7、振荡时间为120 min的条件下,对模拟废水中Cd2+的去除率为98.0%。2-450℃-FA吸附剂对Cd2+的吸附主要受颗粒内扩散控制,吸附过程可用准二级吸附动力学方程很好地描述。Ea为77.22 kJ/mol,吸附过程主要为化学吸附。     

Optimizing Cr(VI) adsorption on activated carbon produced from heavy oil fly ash

In order to explore the beneficial utilization of heavy oil fly ash (HOFA) generated in the power plants, the present study is intended to optimize the chromium(VI) [Cr(VI)] adsorption on activated carbon produced from HOFA. The raw HOFA obtained from a power plant was washed by nitric/hydrochloric acid and activated at 800 °C with a holding time of 60 min to produce fly ash activated carbon (FAC). Phosphoric acid was used as a chemical agent to improve the surface characteristics of the HOFA during the activation process. Batch adsorption experiments were employed to evaluate the effects of different parameters such as initial Cr(VI) concentration, pH, and FAC dose on the removal of Cr(VI) from aqueous solution. A total of 17 adsorption experimental runs were carried out employing the detailed conditions followed the response surface methodology based on the Box–Behnken design. The results indicate that developed FAC has the potential for removing Cr(VI) from wastewater. Under the test conditions, a maximum of 91.51 % Cr(VI) removal efficiency was achieved.     

Utilization of turkey manure as granular activated carbon: physical, chemical and adsorptive properties

The high availability of large quantities of turkey manure generated from turkey production makes it an attractive feedstock for carbon production. Pelletized samples of turkey litter and cake were converted to granular activated carbons (GACs) by steam activation. Water flow rate and activation time were changed to produce a range of activation conditions. The GACs were characterized for select physical (yield, surface area, bulk density, attrition), chemical (pH, surface charge) and adsorptive properties (copper ion uptake). Carbon physical and adsorptive properties were dependent on activation time and quantity of steam used as activant. Yields varied from 23% to 37%, surface area varied from 248 to 472 m(2)/g and copper ion adsorption varied from 0.72 to 1.86 mmol Cu(2+)/g carbon. Copper ion adsorption greatly exceeded the values for two commercial GACs. GACs from turkey litter and cake show considerable potential to remove metal ions from water.     

Preparation and characterization of high surface area activated carbon from pine wood sawdust by fast activation with H<Subscript>3</Subscript>PO<Subscript>4</Subscript> in a spouted bed

Activated carbons were produced from waste pine wood sawdust using fast activation with H₃PO₄ in a spouted bed. In this study, activation temperature was set as 800 °C, and activation time ranged from 1 to 15 min. Experimental results show that sawdust impregnated with higher mass ratio of H₃PO₄ would be agglomerated in spouted bed, and difficult to fluidize. Therefore, an amount of quartz sand was added to assist for good fluidization. Fluidization of particle can improve the BET surface area or micropore volume of activated carbons. High BET surface area activated carbons can be obtained with activation time of only 1–5 min by combining the fluidization and H₃PO₄ fast activation. The obtained activated carbons contained developed pore structure and abundant surface functional groups (carboxyl, carbonyl and P-containing groups) by SEM–EDS, FTIR and XPS techniques. The particles of impregnation ratio of 1:1 can achieve fluidization without adding the quartz sand, which was convenient for experimental operation and even industrial production, and the BET surface area can reach more than 1000 m²/g in activation time of only 5 min.     

Physical and chemical properties study of the activated carbon made from sewage sludge

Preparation of activated carbon from sewage sludge is a promising way to produce a useful adsorbent for pollutants removal as well as to dispose of sewage sludge. The objective of this study was to investigate the physical and chemical properties of the activated carbon made from sewage sludge so as to give a basic understanding of its structure. The activated carbon was prepared by activating anaerobically digested sewage sludge with 5 M ZnCl2 and thereafter pyrolyzing it at 500 degrees C for 2 h under nitrogen atmosphere. The properties investigated in the present study included its surface area and pore size distribution, its elemental composition and ash content, its surface chemistry structure and its surface physical morphology. Furthermore, its adsorption capacities for aqueous phenol and carbontetrachloride were examined. The results indicated that the activated carbon made from sewage sludge had remarkable micropore and mesopore surface areas and notable adsorption capacities for phenol and carbon-tetrachloride. In comparison with commercial activated carbons, it displayed distinctive physical and chemical properties.     

粉煤灰的改性及对刚果红的吸附

分别采用沸水浸泡、酸浸、碱浸和加热的方法对粉煤灰进行改性处理，利用FTIR仪和XRD仪对改性粉煤灰的成分和官能团进行了分析，并利用改性粉煤灰对模拟刚果红废水进行脱色。实验结果表明：碱改性粉煤灰中含有大量官能团，以及NaPl型沸石类物质，能够明显提高粉煤灰对刚果红的吸附性能；与活性炭相比，碱改性粉煤灰具有更高的性价比；在初始刚果红质量浓度为20mg/L、碱改性粉煤灰加入量为50g/L的条件下，废水的脱色率可达87.52%；碱改性粉煤灰对刚果红的吸附过程遵循二级反应动力学，较好地符合Langmuir等温式和Freundlich等温式。     

The development of low cost adsorbents from clay and waste materials: a review

Increased energy consumption due to industrial growth has increased the levels of carbon dioxide (CO₂) emission being released into the atmosphere. CO₂ emission is a type of greenhouse gas which is a major cause of global warming. Since the issue of CO₂ emissions has drawn much attention in recent years, the development of CO₂ capture technology has become a necessity. Although CO₂ adsorbents are still at the early development stage, it has been suggested that CO₂ adsorbents are the most effective technology in controlling CO₂ emissions. Solid adsorbents have great potential as an alternative method to conventional adsorbents in adsorbing CO₂. In this paper, low cost adsorbents including activated carbon, zeolites, mesoporous silica and clays are discussed in terms of adsorbent preparation methods and CO₂ adsorption capacity. The low cost adsorbents are mainly derived from waste materials such as fly ash, steel slag, red mud, bagasses wastes and wood wastes. Besides that, natural resources such as clays have also been applied as low cost CO₂ adsorbents. Surface modifications have also been applied to the low cost adsorbents, including metal ion exchange and amine impregnation to enhance CO₂ adsorption capacity. In the last section, the current status of CO₂ adsorbents is summarized and future trends are discussed briefly to predict the potential materials which can be applied as CO₂ adsorbents.     

Neutralization of an extremely acidic sludge and stabilization of heavy metals in flyash aggregates

An extremely acidic, heavy metal-rich sludge (pH=-1.2) was scrubbed with a Class-F fly ash in order to simultaneously neutralize the acidity and stabilize the heavy metals contained in both wastes. This paper outlines the leaching behavior of the aggregate material generated by scrubbing. For proper fly ash/sludge ratios, the fly ash acted as an outstanding neutralizer for the acidic waste. Leaching of heavy metals from the aggregate samples was below the environmental limits within a pH range between 3 and 9. Subsequent washing of the leached aggregate with acidic CALWET solutions did not result in an additional release of heavy metals. It is proposed that coordinative bonding of the metal cations onto neutral surface sites and electrostatic adsorption led to stabilization of the heavy metals within the aggregate structure below hydrolysis pHs.     

Treatment of olive mill waste water with activated carbons from agricultural by-products

A series of activated carbons prepared by a two-step steam activation of olive stone and solvent extracted olive pulp (SEOP) have been used in an attempt to investigate the total phenol removal and chemical oxygen demand (COD) decrease in olive mill waste water (OMWW). The temperature of carbonization and activation were kept constant at 850 and 800 degrees C, respectively. One of the carbons was prepared by a single-step process at 800 degrees C. Activated carbons have been characterized by adsorption of N2 at 77 K and mercury porosimetry. Their iodine values were also determined. Surface oxides of activated carbons were determined using the Boehm's method. The porosity development and the surface chemistry of carbons were correlated to increasing removal ability of organic molecules. Kinetics of adsorption was evaluated by applying the Lagegren model while adsorption isotherm data were fitted to Langmuir model. Mesoporosity seems to be the key factor for total phenol removal while micoporosity controls the adsorption of total organics as expressed by the COD decrease in OMWW. For carbons with similar structure, the adsorption of phenols or total organics might be affected by the presence of carbonyls.     

Agricultural waste biomass converted to activated carbon as a material for gold processing

Waste biomass in the form of coconut shells was pyrolyzed and activated with steam to produce activated carbons, which were then assessed for their potential for use in the processing of gold. Activated carbons with different amounts of carbon burn-off were prepared by steam activation of carbonized coconut shells. Carbonization of the shells was performed at a pyrolysis temperature of 600?°C and the resulting chars were activated in steam at a gasification temperature of 900?°C and various durations of activation time. Textural characteristics of the derived activated carbons were determined and their effects on gold adsorption from an acidified gold chloride solution were studied. The surface area and porosity of the activated carbons increased with activation time up to 59 wt?% carbon burn-off. A further increase in the burn-off resulted in the loss of structural walls between pores and consequently, a decline in the surface area and porosity of the activated carbons. The gold adsorption capacity and rate of gold adsorption from the gold chloride solution onto the activated carbons were found to increase significantly with the total pore and micropore volumes of the activated carbons.     

Mercury Capture on Fly Ash and Sorbents: The Effects of Coal Properties and Combustion Conditions

The US fleet of coal-fired power plants, with generating capacity of just over 300 GW, is known to be a major source of domestic mercury (Hg) emissions. To address this, in March 2005, the Environmental Protection Agency (EPA) promulgated the Clean Air Mercury Rule (CAMR) to reduce emissions of mercury from these plants. It is generally believed that most of the initial (Phase I) mercury reductions will come as a co-benefit of existing controls used to remove particulate matter (PM), SO₂, and NO _X . Deeper reductions in emissions (as required in Phase II of CAMR) may require the installation of mercury-specific control technology. Duct injection of activated carbon sorbents is the mercury-specific control technology that has been most widely studied and has been demonstrated over a wide range of coal types and combustion conditions. The effectiveness of the mercury control options (both “co-benefit control” and “mercury-specific control”) is significantly impacted by site-specific characteristics such as the combustion conditions, the configuration of existing air pollution controls, and the type of coal burned. This paper identifies the role of coal properties and combustion conditions in the capture of mercury by fly ash and injected sorbents.     

CuCl2改性飞灰吸附气相零价汞

采用CuCl₂对循环流化床锅炉飞灰进行改性,在固定床反应器上对CuCl₂改性飞灰进行了气相零价汞（Hg⁰）吸附实验。考察了CuCl₂负载量和吸附温度对改性飞灰Hg⁰吸附能力的影响,并结合颗粒内扩散模型、准一阶动力学模型、准二阶动力学模型和耶洛维奇模型拟合结果分析该过程的控制步骤。结果表明： CuCl₂改性飞灰的Hg⁰穿透时间远大于未改性飞灰,对Hg⁰的吸附量随CuCl₂负载量的增加而增加;CuCl₂改性飞灰的Hg⁰吸附能力随吸附温度的升高先增大后减小,150 ℃为最佳吸附温度;准二阶动力学模型的拟合值与实验值相关系数最高,且该模型初始吸附速率与实验值最为接近,即准二阶动力学模型更适合于描述CuCl₂改性飞灰的Hg⁰吸附过程。     

复合改性粉煤灰对磷的吸附性能

将粉煤灰（FA）与Na₂CO₃混合焙烧后浸渍负载Fe²⁺,制备了复合改性粉煤灰（CMFA）。通过多种手段对CMFA进行了表征,并将其用于含磷废水的吸附处理。表征结果显示：改性后的粉煤灰表面疏松多孔,比表面积增大了21倍,产生了金属盐类熔出物及羟基氧化铁和羟基官能团。实验结果表明：当初始磷质量浓度为50 mg/L、吸附温度为20 ℃、溶液pH为4.3、CMFA投加量为5 g/L、吸附时间为30 min时,磷去除率可达98.01%,较FA的50.10%大幅提升;20 ℃时,CMFA对磷的饱和吸附量可达22.15 mg/g;用拟二级动力学模型可较准确地描述CMFA对磷的吸附过程,该过程为自发的吸热过程,符合Langmuir等温吸附模型,为以离子交换为主的化学吸附。     

Removal of Cr6 + and Ni2+ from aqueous solution using bagasse and fly ash

Raw bagasse and fly ash, the waste generated in sugar mills and boilers respectively have been used as low-cost potential adsorbents. Raw bagasse was pretreated with 0.1N NaOH followed by 0.1N CH3COOH before its application. These low-cost adsorbents were used for the removal of chromium and nickel from an aqueous solution. The kinetics of adsorption and extent of adsorption at equilibrium are dependent on the physical and chemical characteristics of the adsorbent, adsorbate and experimental system. The effect of hydrogen ion concentration, contact time, sorbent dose, initial concentrations of adsorbate and adsorbent and particle size on the uptake of chromium and nickel were studied in batch experiments. The Sorption data has been correlated with Langmuir, Freundlich and Bhattacharya and Venkobachar adsorption models. The efficiencies of adsorbent materials for the removal of Cr(VI) and Ni(II) were found to be between 56.2 and 96.2% and 83.6 and 100%, respectively. These results were obtained at the optimized conditions of pH, contact time, sorbent dose, sorbate concentration of 100 mg/l and with the variation of adsorbent particles size between 0.075 and 4.75 mm. The order of selectivity is powdered activated carbon > bagasse > fly ash for Cr(VI) removal and powdered activated carbon > fly ash > bagasse for Ni(II) removal.