Arsenic removal from aqueous solutions by adsorption on red mud

Use of red mud, which is a waste product from bauxite processing, has been explored as an alternate adsorbent for arsenic in this study. The tests showed that the alkaline aqueous medium (pH 9.5) favored the removal of As(III), whereas the pH range from 1.1 to 3.2 was effective for As(V) removal. The process of arsenic adsorption follows a first-order rate expression and obeys the Langmuir's model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. It would be advantageous to use this residue as an adsorbent replacing polyvalent metal salts.     

A case study of methomyl removal from aqueous solutions by four natural Albanian clays

This study evaluated the adsorption properties of four Albanian natural clays from the regions of Brari, Currila, Dardha, and Prrenjasi for commercial methomyl from aqueous solutions. Three methomyl concentrations, 0.200, 0.400, and 0.600 mg/ml, were tested at 25°C to study the influence of the insecticide concentration on the adsorption process for each natural clay type. Within 48 hr of contact time, the adsorption pathways of methomyl on the selected clays are well described by a Langmuir‐like adsorption kinetic model and an intraparticle diffusion model. Hydrolysis and desorption inhibit the overall removal process. The increase of methomyl concentration in solution within the first 48 hr leads to linear adsorption increases well described by Langmuir and Freundlich adsorption isotherms and disfavors the desorption step for the Brari, Currila, and Dardha clays. For the methomyl concentration of 0.600 mg/ml, within 24 hr of contact time, the Dardha and Prrenjasi clays reveal 1.471 and 1.956 mg/g methomyl uptake, respectively. The Brari and Currila clays show longer saturation times followed by better methomyl retention. The Dardha and Prrenjasi clays exhibit fast and high adsorption combined with low retention times.     

Activated carbon from Ceiba pentandra hulls, an agricultural waste, as an adsorbent in the removal of lead and zinc from aqueous solutions

The ability of low-cost activated carbon prepared from Ceiba pentandra hulls, an agricultural waste material, for the removal of lead and zinc from aqueous solutions has been investigated. In the batch tests experimental parameters were studied, including solution pH, contact time, adsorbent dose and initial metal ions concentration. The adsorbent exhibited good sorption potential at pH 6.0. Maximum removal of lead (99.5%) and of zinc (99.1%) with 10 g/l of sorbent was observed at 50 mg/L sorbate concentration. Removals of about 60-70% occurred in 10 min, and equilibrium was attained at around 50 min for both metals. The functional groups (CO, SO,-OH) present on the carbon surface were responsible for the adsorption of metal ions. The adsorption parameters were analysed using both the Freundlich and Langmuir models. The data are better fitted by the Freundlich isotherm as compared to Langmuir model, and the adsorption capacities for lead and zinc were 25.5 and 24.1 mg/g, respectively. Kinetics of adsorption obeyed a second order rate equation and the rate constant was found to be 2.71 x 10(-2) and 2.08 x 10(-2) g/mg/min for lead and zinc, respectively. The desorption studies were carried out using dilute HCl, and the effect of HCl concentration on desorption was studied. Maximum desorptions of 85% for lead and 78% for zinc were attained with 0.15 M HCl.     

Arsenic adsorption from aqueous solutions by activated red mud

Heat treatment and acid treatment methods have been tested on red mud to increase its arsenic adsorption capability. The results indicate that the adsorptive capacity of red mud can be increased by acid treatment. This treatment causes sodalite compounds to leach out. As(III) and As(V) adsorption characteristics of activated red mud have similar tendencies with raw red mud. Batch adsorption studies have shown that activated red mud in dosages ranging from 20 to 100 g l(-1) can be used effectively to remove arsenic from aqueous solutions. The process is pH dependent, the optimum range being 5.8-7.5 for As(III) and 1.8-3.5 for As(V). The maximum removals are 96.52% for As(V) and 87.54% for As(III) for solutions with a final pH of 7.25 and 3.50, respectively, for the initial arsenic concentration of 133.5 micromol l(-1) (10 mg l(-1)), activated red mud dosage of 20 g l(-1), contact time of 60 min and temperature of 25 degrees C. The adsorption data obtained follow a first-order rate expression and fit the Langmuir isotherm well. Isotherms have been used to obtain the thermodynamic parameters. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic.     

Removal of ammonium and phosphates from aqueous solutions by biochar produced from agricultural waste

The concern about protecting water quantity and quality is one of the most severe challenges of the twenty-first century since the demand for water resources grows as the population and its needs grow. Additionally, and as expected, most human activities produce wastewater containing undesirable contaminants. On the other hand, the generation of agricultural waste and its inappropriate disposal causes further problems. Current wastewater treatment methods involve a combination of physical and chemical processes, technologies, and operations to remove pollutants from effluents; adsorption is an excellent example of an effective method for wastewater treatment, and biochar is currently one of the most valuable adsorbents. This review focuses on new research about applying biochar produced from agricultural waste as a low-cost and environmentally friendly method for removing ammonium and phosphates from aqueous solutions.

     

Removing cadmium from aqueous solutions utilizing agricultural wastes

The purpose of this study was to determine the cadmium (Cd) biosorption capacities of several agricultural wastes from aqueous solutions. Samples were tested unaltered and after hydrochloric acid treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cd solutions. Desorption studies were performed to determine if the removed Cd could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cd biosorption cycles. The results of this study demonstrate a wide range of Cd biosorption proficiencies ranging from 33 to 100% removal. The parameters that resulted in higher Cd removal include higher sample dose, higher pH, and lower Cd solution concentration. Desorption results showed a 36–56% Cd recovery rate. Reused AWS were effective at removing Cd during subsequent trials. Therefore, all AWS types tested in this study can be reused for additional Cd biosorption cycles. Hence, it is possible that using AWS for metal treatment could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cd biosorption cycle.     

Orange peel as an adsorbent in the removal of acid violet 17 (acid dye) from aqueous solutions

The effectiveness of orange peel in adsorbing Acid violet 17 from aqueous solutions has been studied as a function of agitation time, adsorbent dosage, initial dye concentration and pH. The adsorption follows both Langmuir and Freundlich isotherms. The adsorption capacity Q0 was 19.88 mg/g at initial pH 6.3. The equilibrium time was found to be 80 min for 10, 20, 30 and 40 mg/L, dye concentration respectively. A maximum removal of 87% was obtained at pH 2.0 for an adsorbent dose of 600 mg/50 ml of 10 mg/L dye concentration. Adsorption increases with increase in pH. Maximum desorption of 60% was achieved in water medium at pH 10.0.     

Sunflower stalk, an agricultural waste, as an adsorbent for the removal of lead and cadmium from aqueous solutions

Sunflower residue, an agricultural waste material for the removal of lead (Pb) and cadmium (Cd) from aqueous solutions were investigated using a batch method. Adsorbent was prepared by washing sunflower residue with deionized water until the effluent was colorless. Batch mode experiments were carried out as a function of solution pH, adsorbent dosage, initial concentration and contact time. The results indicated that the adsorbent showed good sorption potential and maximum metal removal was observed at pH 5. Within 150 min of operation about 97 and 87 % of Pb and Cd ions were removed from the solutions, respectively. Lead and Cd sorption curves were well fitted to the modified two-site Langmuir model. The adsorption capacities for Pb and Cd at optimum conditions were 182 and 70 mg g^?1, respectively. The kinetics of Pb and Cd adsorption from aqueous solutions were analyzed by fitting the experimental data to a pseudo-second-order kinetic model and the rate constant was found to be 8.42 × 10^?2 and 8.95 × 10^?2 g mg^?1 min^?1 for Cd and Pb, respectively. The results revealed that sunflower can adsorb considerable amount of Pb and Cd ions and thus could be an economical method for the removal of Pb and Cd from aqueous systems.     

Biosorption of copper from aqueous solutions utilizing agricultural wastes

The purpose of this study was to determine the copper (Cu) biosorption capacities of several agricultural wastes from aqueous solutions. Samples of agricultural wastes were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cu solutions. Desorption studies were performed to determine if the removed Cu could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cu biosorption cycles. The results of this study demonstrate a wide range of Cu biosorption proficiencies ranging from 0% to 100% removal. The parameters that resulted in higher Cu removal include higher pH and lower Cu solution concentration. Desorption results showed a 58% to 86% Cu recovery rate. Three of the five reused AWS were effective at removing Cu during subsequent trials. Therefore, these AWS types can be reused for additional Cu biosorption cycles. Hence, it is possible that using those AWS for metal treatment could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cu biosorption cycle.     

Utilizing agricultural wastes to remove hexavalent chromium from aqueous solutions

The purpose of this study was to determine the hexavalent chromium (Cr^VI) biosorption capacities of several agricultural wastes from aqueous solutions. Samples were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cr^VI solutions. Desorption studies were performed to determine if the removed Cr^VI could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cr^VI biosorption cycles. The results of this study demonstrate a wide range of Cr^VI biosorption proficiencies ranging from 13 to 98 percent removal. The parameters that resulted in higher Cr^VI removal include HCl treatment, higher sample dose, lower Cr^VI solution concentration, and lower mixing temperature. Desorption results showed an 8 to 25 percent Cr^VI recovery rate. Reused AWS were effective at removing Cr^VI during subsequent trials. Therefore, all AWS can be reused for additional Cr^VI biosorption cycles. Hence, these could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cr^VI biosorption cycle.     

Mercury flows in a zinc smelting facility in South Korea

To prepare for the international mercury convention, the characteristics of mercury emissions from a zinc smelting facility in South Korea have been reviewed and a material flow analysis (MFA) has been conducted in this research. As inputs into the mercury MFA study, zinc ores and sulfuric acid were examined, whereas wastewater sludge, effluence water, spent catalyst, and emissions from the casting and roasting processes were examined as outputs. Mercury concentrations extracted from end products like zinc ingots, cadmium ingots, and sulfuric acid were then analyzed. Our results showed that the wastewater sludge discharged from the zinc smelting process had a relatively higher concentration of mercury, indicating that the concentration of mercury was further enriched in the wastewater sludge. The wastes discharged through the zinc smelting process should be thoroughly controlled, as results of the MFA showed that approximately 89 % of the mercury contained in the original input was later found in the waste. According to this study, the higher the concentration of mercury within zinc ores at the input stage, the higher is the mercury concentration found in the wastewater sludge at the output stage.     

Cr(VI) reduction in aqueous solutions by using copper smelter slag

The ability of Copper Smelter Slag (CSS) to reduce Cr(VI) in aqueous solutions has been investigated. The extent of reduction is dependent on the amounts of acid and reductant, contact time, Cr(VI) concentration, temperature of the solution and particle size of CSS. The amount of acid is the most important variable affecting the reduction process. When twice the amount of acid required with respect to Cr(VI) was used, Cr(VI) in 100 ml solution (100 mg/l) was completely reduced in a contact period less than 5 min by a 10 g/l dosage of CSS. Reduction efficiency increased with increase in temperature of solution, showing that the process is endothermic. Reduced chromium, and iron and other metals dissolved from CSS were effectively precipitated by using NaOH or calcinated carbonatation sludge from sugar plant.     

Ammonium removal from landfill leachate by chemical precipitation

The landfill leachate in Hong Kong usually contains quite high NH₄⁺–N concentration, which is well known to inhibit nitrification in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH₄⁺–N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH₄⁺–N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH₄⁺–N in the leachate collected from a local landfill in Hong Kong as magnesium ammonium phosphate (MAP). In the experiment, three combinations of chemicals, MgCl₂·6H₂O+Na₂HPO₄·12H₂O, MgO+85% H₃PO₄, and Ca(H₂PO₄)₂·H₂O+MgSO₄·7H₂O, were used with the different stoichiometric ratios to generate the MAP precipitate effectively. The results indicated that NH₄⁺–N contained in the leachate could be quickly reduced from 5618 to 112 mg/l within 15 min, when MgCl₂·6H₂O and Na₂HPO₄·12H₂O were applied with a Mg²⁺:NH₄⁺:PO₄³⁻ mol ratio of 1:1:1. The pH range of the minimum MAP solubility was discovered to be between 8.5 and 9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl₂·6H₂O and Na₂HPO₄·12H₂O, which may affect microbial activity in the following biological treatment processes. The other two combinations of chemicals [MgO+85% H₃PO₄ and Ca(H₂PO₄)2·H₂O+MgSO₄·7H₂O] could minimise salinity after precipitation, but they were less efficient for NH₄⁺–N removal, compared with MgCl₂·6H₂O and Na₂HPO₄·12H₂O. COD had no significant reduction during this precipitation. It was found that the sludge of MAP generated was easily settled within 10 min to reach its solids content up to 27%. The other characteristics including capillary suction time (CST) and dry density (DD) of the MAP sludge were also tested. The experimental results indicate that the settled sludge is quite solid and can be directly dumped at a landfill site even without any further dewatering treatment.     

Immobilization of radioactive waste by cementation with purified kaolin clay

A study is undertaken to determine the waste immobilization performance of low-level wastes in cement-clay mixtures. Liquid low-level wastes are precipitated using chemical methods, followed by solidification in drums. Solidification is done using cementation processes. Long-term leaching rates of the radionuclides are used as indicators of immobilization performance of solidified waste forms. In addition to evaluating the effects of kaolin clay on the leaching properties of the cemented waste forms, the effect of addition of kaolin on the strength of the cemented waste form is also investigated. The long term leaching tests show that inclusion of kaolin in cement reduces the leaching rates of the radionuclides significantly. However, clay additions in excess of 15 wt.% causes a significant decrease in the hydrolytic stability of cemented waste form. It is found that the best waste isolation, without causing a loss in the mechanical strength, is obtained when the kaolin content in cement is 5%.     

Mercury cleanup: The commercial application of a new mercury removal/recovery technology

Efficient, economical treatment of mercury-contaminated soils and industrial wastes requires a treatment process that reduces mercury content to near background levels (<1 ppm) and recovers the removed mercury in pure recyclable form without producing liquid, solid, or gaseous secondary wastes. This article reviews the results achieved using a medium-temperature thermal desorption process developed and commercialized by Mercury Recovery Services, Inc. (MRS) that has successfully achieved these goals.     

Novel Mercury Oxidant and Sorbent for Mercury Emissions Control from Coal-fired Power Plants

The authors have successfully developed novel efficient and cost-effective sorbent and oxidant for removing mercury from power plant flue gases. These sorbent and oxidant offer great promise for controlling mercury emissions from coal-fired power plants burning a wide range of coals including bituminous, sub-bituminous, and lignite coals. A preliminary analysis from the bench-scale test results shows that this new sorbent will be thermally more stable and cost-effective in comparison with any promoted mercury sorbents currently available in the marketplace. In addition to the sorbent, an excellent elemental mercury (Hg(0)) oxidant has also been developed, and will enable coal-fired power plants equipped with wet scrubbers to simultaneously control their mercury emissions as well as their sulfur oxides emissions. This will work by converting all elemental mercury to an oxidized form which will be removed by the wet scrubber. This will result in significant cost savings for mercury emissions control to the atmosphere, and will help in keeping electric costs low. The sorbent and oxidant will benefit from the utilization of a waste stream from the printed circuit board (PCB) industry, and would thus be environmentally beneficial to both of the utility and electronics industries. The sorbent also demonstrated thermal stability up to 350°C, suggesting a possibility of an application in pulverized coal-fired power plants equipped with hot-side electrostatic precipitators and coal gasification plants.     

Siloxanes removal from biogas by high surface area adsorbents

Biogas utilized for energy production needs to be free from organic silicon compounds, as their burning has damaging effects on turbines and engines; organic silicon compounds in the form of siloxanes can be found in biogas produced from urban wastes, due to their massive industrial use in synthetic product, such as cosmetics, detergents and paints.Siloxanes removal from biogas can be carried out by various methods (Mona, 2009, Ajhar et al., 2010, Schweigkofler and Niessner, 2001); aim of the present work is to find a single practical and economic way to drastically and simultaneously reduce both the hydrogen sulphide and the siloxanes concentration to less than 1 ppm. Some commercial activated carbons previously selected (Monteleone et al., 2011) as being effective in hydrogen sulfide up taking have been tested in an adsorption measurement apparatus, by flowing the most volatile siloxane (hexamethyldisiloxane or L2) in a nitrogen stream, typically 100–200 ppm L2 over N₂, through an activated carbon powder bed; the adsorption process was analyzed by varying some experimental parameters (concentration, grain size, bed height). The best activated carbon shows an adsorption capacity of 0.1 g L2 per gram of carbon. The next thermogravimetric analysis (TGA) confirms the capacity data obtained experimentally by the breakthrough curve tests.The capacity results depend on L2 concentration. A regenerative carbon process is then carried out by heating the carbon bed up to 200 °C and flushing out the adsorbed L2 samples in a nitrogen stream in a three step heating procedure up to 200 °C. The adsorption capacity is observed to degrade after cycling the samples through several adsorption–desorption cycles.