Brian E. Reed

Modeling Cadmium Adsorption by Activated Carbon Using the Langmuir and Freundlich Isotherm Expressions

Abstract Cadmium adsorption isotherms were conducted using two commercially available powdered activated carbons (PACs). Isotherms were conducted at several pH values and metal and carbon concentrations. Both PACs removed significant amounts of cadmium, and removal was a strong function of solution pH: increasing the solution pH increased cadmium adsorption. Adsorption data at a specific pH were successfully modeled using both the Langmuir and Freundlich isotherms. Adsorption and surface precipitation were hypothesized to be the operative removal mechanisms. Cadmium removal is strongly related to the carbons pHzpc, acid-base characteristics, and surface charge-pH relationship. Surface area, an important adsorption parameter for organic adsorbates, does not appear to influence metal removal strongly.

Removal of lead and cadmium from aqueous waste streams using granular activated carbon (GAC) columns

The use of granular activated carbon (GAC) columns to treat metal-bearing wastewaters was investigated. Synthetic wastewaters containing Pb and Cd ( 10 or 50 mg/L), acetic acid (0.001 N ) or EDTA (1:O.l or 1:l Me:EDTA molar ratios) were studied. For metalonly and metalacet ic acid experiments, significant quantities (as high as 325 bed volumes (BV) ) of wastewater were treated prior to breakthrough (C, = 0.03 C,). X / M values were as high as about 30 mg Pb/g carbon. For EDTA experiments, C, was always> 0.03 C,. The amount of metal not removed corresponded to the amount that was complexed by EDTA. Column pH is the critical parameter influencing column performance. The increase in effluent metal concentration corresponded with the decrease in column pH. GAC columns were successfully regenerated using a I L ( = 8 B V ) 0.1 N HN03 rinse followed by a 1 L 0.1 N NaOH rinse. Column performance was not adversely affected by regeneration. When the regeneration step was used on virgin carbon, a dramatic improvement in column performance was observed and was attributed to the increase in carbon surface p H (pH= 11) and the deposition of OHin the pore liquid. Possible removal mechanism are precipitation on the carbon surface and in the pore liquid, and adsorption.

Metal Adsorption by Activated Carbon: Effect of Complexing Ligands, Competing Adsorbates, Ionic Strength, and Background Electrolyte

Abstract Cadmium and nickel adsorption isotherms were performed using three activated carbons in ligand-free systems and in the presence of EDTA, succinic acid, PO4 (Ni only), NH4BF4 (Cd only), competing metals (Ni and Cd), and differing ionic strengths and background electrolytes. Generally, all carbons removed metals from the ligand-free systems. Four scenarios were forwarded which described metal adsorption in the presence of various organic and inorganic compounds. The effect of organic and inorganic ligands on metal removal was dependent on the carbon, metal, and ligand type and concentration. The presence of a second heavy metal did not affect removal of the primary metal ion. Increasing ionic strength decreased metal removal for all carbons and metals investigated while the type of background electrolyte had no effect on metal removal.

Retention and Release of Lead by a Very Fine Sandy Loam. I. Isotherm Modeling

Abstract The retention of lead by a very fine sandy loam was investigated. Aqueous lead concentrations between 10 and 1000 mg/L and soil concentrations ranging from 10 to 167 g/L were used. Lead retention by the soil was a strong function of pH. The width of the pH—adsorption edge decreased with increasing lead concentration. Experimental results were modeled using the Langmuir, Freundlich, and BET isotherms. Only the Langmuir and Freundlich isotherms successfully represented the experimental results. The role of surface precipitation was assumed to be small because of the failure of the BET isotherm to adequately predict metal retention. The Freundlich isotherm provided the best fit because a maximum surface concentration was usually not observed. Langmuir and Freundlich isotherms parameters varied in a way that suggested that the average binding energy and the distribution of bond strengths increased with increasing pH. The isotherm expressions determined in this study can be used as source-sink terms i...

Modeling surface acidity of two powdered activated carbons: Comparison of diprotic and monoprotic surface representations

Abstract Powdered activated carbon (PAC) can behave as a weak acid in solution. Historically, the amphoteric nature of hydrous solids has been modeled as a single weak diprotic acid. To determine if the single diprotic representation was the most appropriate description of the PAC surface, two commercially available PACs underwent acidimetric-alkalimetric and NaNO 3 titrations. The surface complex formation (SCF) model, a variation of a soluble equilibrium chemical model, was used to simulate experimental titration curves using several surface representations. A three-monoprotic site model was chosen to represent the amphoteric nature of both PACs studied, based on the following criteria: the goodness of fit of model results; the coherence of the representations to previously published results; and the agreement of surface site representations at different ionic strengths for the same PAC. Surface acidity parameters ( pH zpc , acidity coefficients and number of surface sites) and surface speciation diagrams are presented.

Electronic (EK) remediation of a contaminated soil at several Pb concentrations and applied voltages

Abstract The in situ remediation of a lead‐contaminated silt loam by electrokinetic (EK) soil flushing was studied. Two initial soil Pb concentrations (150 and 1000 mg/kg of Pb) and applied voltages (30 and 60 V) were investigated. The EK soil flushing process was less efficient for the 150 mg/kg of Pb soils despite these tests being operated for longer durations, having larger EO flows and energy inputs, and lower soil pHs. The decrease in effectiveness was attributed to a larger average metal‐soil binding energy for the lower contaminated soil. Increasing the voltage increased the EO flow, current, energy input (kW‐hr/kg of soil), and provided a more evolved low pH front, resulting in more soil being remediated. There appeared to be a correlation between the amount of EO flow and the desorption and transport of soil‐bound lead. Because complete soil remediation did not occur in any of the tests, the final energy input per kilogram of soil could not be calculated.

Evaluation of sorbent amendments for in situ remediation of metal‐contaminated sediments

The present study evaluated sorbent amendments for in situ remediation of sediments contaminated with two divalent metals. A literature review screening was performed to identify low-cost natural mineral-based metal sorbents and high-performance commercial sorbents that were carried forward into laboratory experiments. Aqueous phase metal sorptivity of the selected sorbents was evaluated because dissolved metals in sediment porewater constitute an important route of exposure to benthic organisms. Based on pH-edge sorption test results, natural sorbents were eliminated due to inferior performance. The potential as in situ sediment amendment was explored by comparing the sorption properties of the engineered amendments in freshwater and saltwater (10 PPT salinity estuarine water) matrices. Self-assembled monolayers on mesoporous supports with thiols (Thiol-SAMMS) and a titanosilicate mineral (ATS) demonstrated the highest sorption capacity for cadmium (Cd) and lead (Pb), respectively. Sequential extraction tests conducted after mixing engineered sorbents with contaminated sediment demonstrated transfer of metal contaminants from a weakly bound state to a more strongly bound state. Biouptake of Cd in a freshwater oligochaete was reduced by 98% after 5-d contact of sediment with 4% Thiol-SAMMS and sorbed Cd was not bioavailable. While treatment with ATS reduced the small easily extractable portion of Pb in the sediment, the change in biouptake of Pb was not significant because most of the native lead was strongly bound. The selected sorbents added to sediments at a dose of 5% were mostly nontoxic to a range of sensitive freshwater and estuarine benthic organisms. Metal sorbent amendments in conjunction with activated carbon have the potential to simultaneously reduce metal and hydrophobic contaminant bioavailability in sediments.

A Laboratory-Scale Study of Applied Voltage on the Electrokinetic Separation of Lead from Soils

ABSTRACT The application of electrokinetic (EK) soil-flushing technology to the separation of lead from a nonsynthetic, fine-grained, low permeability soil was examined. In these laboratory-scale experiments the effects of applied voltage (30 and 60 V DC) on cumulative electroosmotic (EO) flow, charge-input, and lead removal were investigated. To develop a more generalized cause-effect relationship, these parameters were studied using three anode/cathode reservoir conditioning schemes: NaNO3/NaNO3, NaNO3/HAc (acetic acid), and HCl/HAc. Charge-input and cumulative EO flow generally increased when the applied voltage was raised. When reservoir pH controls were used, results were more consistent with theoretically predicted outcomes. Increasing the applied voltage increased the electrolysis of water, which increased the fluid conductivity and charge-input. Although cumulative EO flow increased in proportion to the voltage, the advantage of operating at a higher applied voltage diminished as the amount of lea...

NaOH Regeneration of Pb and Phenol-Laden Activated Carbon. I. Batch Study Results

Abstract Granular activated carbon (GAC) has been used to remove organics and metals simultaneously from wastewaters (4). For a regeneration procedure to be effective on GAC containing both metals and organics, it must remove both the metals and organic compounds. In this study, GAC saturated with Pb and phenol was regenerated using an NaOH rinse in batch mode. Four variables were investigated: 1) regenerant concentration (0, 0.1, and 1.0 N), 2) regenerant to carbon mass ratio (5:1 and 10:1), 3) regenerant temperature (22 and 80°C), and 4) regeneration time (0.33, 1, 3, 7, and 21 days). Maximum regenerations of 47% for Pb and 48% for phenol were observed. The 1.0 N NaOH regenerated a higher percentage of both Pb and phenol when compared to the other regenerants. The 10:1 regenerant to carbon ratio resulted in increased regeneration over the 5:1 regenerations. Pb regeneration was slightly higher at 80°C than at 22°C whereas phenol regeneration was slightly lower at 80°C than at 22°C. Maximum regenerations ...

Investigation of Emulsified Oil Wastewater Treatment with Polymers

Abstract Wastewater from metal industry hot milling operations contains oil primarily from coolant sprayed on metal strips to dissipate heat during the rolling of metals. The emulsified oil wastewater for this study was withdrawn from two holding ponds where free oil would rise to the surface and was removed periodically, and used as influent for the chemical addition (CA)-gravity separation (GS) process. The principal objective of this research was to evaluate the effectiveness of different polymer addition systems through a CA-GS process for oil/grease (O/G) and total suspended solids (TSS) removal. Polymers from two corporations were investigated. A dual polymer system was recommended and supplied by Calgon Corporation—a cationic polymer (W-2923) to break the emulsion and an anionic polymer (POL-Z-E 2706) to enhance coagulation. A single polymer system was recommended and supplied by Grace Dearborn (GD) Corporation—a cationic polymer (KLAR-AID 2400) as a coagulant. Two types of experiments were perform...