Mitchell M. Johns

Surface functional groups on acid-activated nutshell carbons

Nutshells from agriculturally important nut crops (almond, black walnut, English walnut, macadamia nut and pecan) were converted to granular activated carbon using phosphoric acid activation in nitrogen or air. Surface functional groups (carbonyl, phenols, lactones, carboxyl) were quantified by titration with bases of different ionization potential. The degree of copper uptake was correlated with the presence of various functional groups on these carbons. The results indicate that acid-activation strategies which provide the greatest contact of nutshells with air during carbonization and activation also have the greatest quantity of surface functional groups and the highest copper uptake. Also, the type of nutshell used for activated carbon production has little effect on the types of surface functional groups produced and subsequent copper adsorption. This study demonstrates that a judicious choice of activation strategy for nutshell precursors can produce activated carbons with numerous surface functional groups and high copper adsorption activity.

Agricultural by-products as granular activated carbons for adsorbing dissolved metals and organics

Surplus, low value agricultural by-products can be made into granular activated carbons (GACs) which are used in environmental remediation. This study characterized and evaluated GACs, made from these feedstocks, as effective removers of organics and metals from water. The by-products included soft lignocellulosics such as rice straw, soybean hull, sugarcane bagasse, peanut shell, and harder materials such as pecan and walnut shells. The softer materials were combined with a binder, molasses, to produce briquettes and pellets. The precursors were CO 2 - or steam-activated, and subsequent treatments included oxidation to enhance metal adsorption. Many of the GACs had acceptable physical GAC attributes, such as durability, for commercial usage. GACs made from pecan and walnut shells adsorbed higher levels of benzene, toluene, methanol, acetonitrile, acetone, and 1,4-dioxane from an aqueous mixture than commercial GACs. Neither CO 2 nor steam activation was particularly advantageous in enhancing metal adsorption. Oxidation using O 2 -N 2 gas increased metal adsorption while (NH 4 )S 2 O 8 solution did not. In a copper solution, oxidized GACs made from soybean hull had three to four times the Cu(II) adsorption capacity of metal-adsorbing, commercial GACs. Oxidized GACs made from soybean hull, sugarcane bagasse, peanut shell, and rice straw adsorbed from a mixture higher amounts of Pb(II), Cu(II), Ni(II), Cd(II) and Zn(II) than any commercial GACs. Commercial GACs adsorbed only Pb(II), Cu(II) and Cd(II). The GACs made from the agricultural by-products have considerable potential for adsorption of organics and metals of environmental concern.

Enhanced metal adsorption by soybean hulls modified with citric acid

Abstract A method was developed to enhance metal ion adsorption of soybean hulls for wastewater treatment using copper ion (Cu2+) as a typical metal ion. Hulls, extracted with 0.1 N NaOH, were modified with different citric acid (CA) concentrations (0.1-1.2 M) at 120°C for 90 min. CA-modified hulls had adsorption capacities for Cu2+ from 0.68 to 2.44 mmoles/g, which was much higher than for unmodified hulls (0.39 mmoles/g). The total negative charge for these hulls also increased with increasing CA concentration and was about twice the copper ion adsorption capacity at all CA concentrations. The need for NaOH (base) extraction (BE) before CA modification was examined. CA-modified, non-extracted (NE) and CA-modified, BE hulls were compared for adsorption kinetics and adsorption capacity. Base extraction resulted in modified hulls with faster adsorption kinetics and slightly lower adsorption capacity for copper ion than NE hulls. For BE, CA-modified hulls, increasing the temperature from 25°C to 60°C appeared to have no effect on the rate of copper ion removal from solution. CA modification of soybean hulls greatly enhanced metal ion removal and resulted in a product with possible commercial potential for metal ion remediation.

Acid-activated carbons from almond shells: physical, chemical and adsorptive properties and estimated cost of production.

Abstract A series of phosphoric-acid activated carbons were made from almond shells using six different activation or activation/oxidation methods. The carbons were compared to each other and to two commercial carbons in an effort to ascertain the relative value of the carbons in terms of yield, surface area, attrition, surface functional groups, organic uptake, metal uptake, as well as estimated cost of production. Of the six methods investigated, the method that produced the best overall performing almond shell carbon and least expensive carbon in terms of production cost was the “Air-Activation” method. This method involved the simultaneous activation and oxidation of almond shells under an air atmosphere.

Granular activated carbons from nutshells for the uptake of metals and organic compounds

Abstract Almond and pecan shells were chosen as hard, lignocellulosic precursors for the production of granular activated carbons (GACs) in order to create carbons for the adsorption of both organic compounds and metals. They were activated either chemically, with H 3 PO 4 , or physically, with CO 2 , under a variety of conditions. Following activation, a portion of the GACs were oxidized with air. The acid-activated samples had higher BET surface areas and greater product yields than the CO 2 -activated carbons. Unoxidized, CO 2 -activated carbons generally sequestered more Cu 2+ from solution than the unoxidized acid-activated GACs, when evaluated in batch assays at pH 4.8. Oxidative treatment, however, improved Cu 2+ adsorption in both types of carbon to levels significantly greater than comparable commercial carbons. Nutshell-based carbons were also examined for their ability to adsorb a variety of low molecular weight organic compounds with differing polarities. For CO 2 -activated pecan shell carbons there was a distinct increase in organic uptake that was usually not altered by oxidation. Both acid- and CO 2 -activated pecan shell carbons took up similar amounts of the non-polar benzene and toluene, but the CO 2 -activated carbons took up more polar compounds. There were several GACs that outperformed commercial carbons in their ability to adsorb significant quantities of Cu 2+ or organics on the same carbon. Our data show that nutshells provide a plentiful and inexpensive precursor for the production of GACs which may be competitive with commercial carbons in wastewater or potable water treatment.

Agricultural by-products as metal adsorbents : Sorption properties and resistance to mechanical abrasion

Defatted rice bran, soybean and cottonseed hulls were evaluated for their sorption properties and resistance to mechanical abrasion in consideration of their potential use as commercial metal adsorbents. These by-products were evaluated using both laboratory prepared solutions and metal plating wastewater for their ability to adsorb Zn(II) and/or Cu(II) and Ni(II). Extrusion stabilized, pilot plant-prepared brans had greater adsorption capacities and adsorption efficiencies than expander stabilized, commercially available bran. All rice brans possessed low mechanical abrasion resistance in batch applications. NaOH- and HCl-washed soybean and cottonseed hulls had generally higher adsorption efficiencies than water-washed (control) hulls, but had higher or lower adsorption capacities, respectively, than water-washed hulls. Heat-treated cottonseed and soybean hulls had lower adsorption properties than water-washed hulls. Unlike rice bran, both soybean and cottonseed hulls were found to have high mechanical abrasion resistance in batch applications. Reuse of hulls after one adsorption/desorption (sorption) cycle resulted in a large decrease in adsorption capacity which classified hulls as single-use adsorbents when desorbed with HCl.

Phosphoric acid activation of nutshells for metals and organic remediation: Process optimization

Almond, pecan, English walnut, black walnut and macadamia nut shells were chosen as hard, lignocellulosic precursors for the production of granular activated carbons (GACs). They were activated with H3PO4 under a variety of conditions. Following activation, a portion of each GACs was oxidized in air at 300°C for 4 h in order to create a carbon surface presumably with more oxygen functional groups for the adsorption of metal cations. Also investigated was a streamlining of the production techniques used. Several of the samples were subjected to a ‘Continuous’ process in which the carbon was activated and upon cooling to 300°C was oxidized with air. Beyond this activation, methods were developed wherein the activation process took place under air and without a discrete, separate oxidation step. These processes were designed to determine if any of the carbons capabilities would be lost or enhanced in comparison to the more standard activate–cool–wash–oxidize method. The carbons produced from these various activation/oxidation methods consistently, and without regard to precursor composition, sequestered over 90% of available copper from a 3 mM copper chloride test solution and often adsorbed organic contaminants as effectively as some commercial carbons.

The effect of binders and agricultural by-products on physical and chemical properties of granular activated carbons

Four binders (coal tar, sugarcane molasses, sugar beet molasses, corn syrup) were mixed with three agricultural by-products (rice hulls, rice straw, sugarcane bagasse) in different combinations and these mixtures transformed into granular activated carbons (GACs). GACs were evaluated for the physical properties of burn-off/yield, surface area, bulk density and hardness and the chemical properties of pH and ash. These properties, except for burn-off/yield, were compared to the same properties of two commercial reference carbons made from bituminous coal with coal tar binder. The results show that GACs made with corn syrup as binder exhibited surface areas, bulk densities, hardness, pH and ash values closest to the reference carbons. The presence of a specific by-product appeared less important than the presence of a specific binder in determining the physical and chemical characteristics of the GACs.

Removal of sugar colorants by granular activated carbons made from binders and agricultural by-products

Twenty-four granular activated carbons (GACs) made from mixtures of four binders (coal tar, sugarcane molasses, sugar beet molasses, corn syrup) and three agricultural by-products (rice hulls, rice straw, sugarcane bagasse) were evaluated for their ability to remove sugar colorants (molasses color removal, sugar decolorization). These properties were compared to the same properties of two commercial reference carbons. GACs made from sugarcane bagasse, in general, possessed the best ability to remove sugar colorants and were closest to the reference carbons in this regard. In fact, the four highest ranked GACs all used bagasse as a feedstock along with four different binders. Therefore, the ability to remove sugar colorants appears to be by-product dependent with the binder playing a minor role.