Recovery of Silver Using Adsorption Gels Prepared from Microalgal Residue Immobilized with Functional Groups Containing Sulfur or Nitrogen.

Although biodiesel oil extracted from microalgae attracts much attention as one of the most promising green energies, its high production cost is a big problem, impeding its extensive use. In order to lower the production cost, the effective use of microalgal residue after extracting biofuel was investigated as a feed material of functional materials. In the present work, a new adsorbent for silver(I) was prepared by immobilizing functional groups of polyethylene-polyamine or dithiooxamide, which exhibita high affinity for soft Lewis acids such as silver(I) ions. Their adsorption behaviors for silver(I) were investigated from aqueous nitrate and acidothiourea media. The effects of the concentrations of nitrate and thiourea, as well as of sulfuric acid, were qualitatively interpreted. From the study of adsorption isotherms on these gels, they were found to exhibita higher adsorption capacity than the majority of those reported to date.

Biosorbents for Removing Hazardous Metals and Metalloids.

Biosorbents for remediating aquatic environmental media polluted with hazardous heavy metals and metalloids such as Pb(II), Cr(VI), Sb(III and V), and As(III and V) were prepared from lignin waste, orange and apple juice residues, seaweed and persimmon and grape wastes using simple and cheap methods. A lignophenol gel such as lignocatechol gel was prepared by immobilizing the catechol functional groups onto lignin from sawdust, while lignosulfonate gel was prepared directly from waste liquor generated during pulp production. These gels effectively removed Pb(II). Orange and apple juice residues, which are rich in pectic acid, were easily converted using alkali (e.g., calcium hydroxide) into biosorbents that effectively removed Pb(II). These materials also effectively removed Sb(III and V) and As(III and V) when these were preloaded with multi-valent metal ions such as Zr(IV) and Fe(III). Similar biosorbents were prepared from seaweed waste, which is rich in alginic acid. Other biosorbents, which effectively removed Cr(VI), were prepared by simply treating persimmon and grape wastes with concentrated sulfuric acid.

Adsorptive removal of cesium using bio fuel extraction microalgal waste.

An adsorption gel was prepared from microalgal waste after extracting biodiesel oil by a simple chemical treatment of crosslinking using concentrated sulfuric acid. The adsorbent exhibited notably high selectivity and adsorption capacity towards Cs(+) over Na(+) from aqueous solutions, within the pH range of slightly acidic to neutral. The adsorption followed Langmuir isotherm and the maximum adsorption capacity of the gel for Cs(+) calculated from Langmuir model was found to be 1.36 mol kg(-1). Trace concentration of Cs(+) ions present in aqueous streams was successfully separated from Na(+) ions using a column packed with the adsorbent at pH 6.5. The adsorption capacity of the gel towards Cs(+) in column operation was 0.13 mol kg(-1). Although the adsorbed Cs(+) ions were easily eluted using 1M hydrochloric acid solution, simple incineration is proposed as an alternative for the treatment of adsorbent loaded with radioactive Cs(+) ions due to the combustible characteristics of this adsorbent.

Preparation of novel alginate based anion exchanger from Ulva japonica and its application for the removal of trace concentrations of fluoride from water.

A green seaweed, Ulva japonica, was modified by loading multivalent metal ions such as Zr(IV) and La(III) after CaCl2 cross-linking to produce metal loaded cross-linked seaweed (M-CSW) adsorbents, which were characterized by elemental analysis, functional groups identification, and metal content determination. Maximum sorption potential for fluoride was drastically increased after La(III) and Zr(IV) loading, which were evaluated as 0.58 and 0.95 mmol/g, respectively. Loaded fluoride was quantitatively desorbed by using dilute alkaline solution for its regeneration. Mechanism of fluoride adsorption was inferred in terms of ligand exchange reaction between hydroxyl ion on co-ordination sphere of the loaded metal ions of M-CSW and fluoride ion in aqueous solution. Application of M-CSW for the treatment of actual waste plating solution exhibited successful removal of fluoride to clear the effluent and environmental standards in Japan, suggesting high possibility of its application for the treatment of fluoride rich waste water.

Adsorptive removal of fluoride from aqueous medium using a fixed bed column packed with Zr(IV) loaded dried orange juice residue.

The potential of the adsorbent prepared from DOJR marketed as cattle food in Japan was identified as an efficient and low cost adsorbent for fluoride using fixed bed column. DOJR was loaded with Zr(IV) ions to develop active adsorption sites for fluoride. Fluoride adsorption performance of column packed with Zr(IV) loaded DOJR was assessed under variable operating conditions such as Zr(IV) loading temperature, initial fluoride concentration, bed depth, initial pH, and flow rate. Breakthrough curve modeling showed that Thomas and bed depth service time (BDST) models were in good agreement with the experimental data. Application of adsorbent investigated in this study to the treatment of actual waste plating solution containing fluoride ion showed successful removal below acceptable standard in Japan using a fixed bed column, hence, Zr(IV)-DOJR can be expected to be a promising candidate for the treatment waste water containing trace amount of fluoride ion in fixed bed column.

N-aminoguanidine modified persimmon tannin: a new sustainable material for selective adsorption, preconcentration and recovery of precious metals from acidic chloride solution.

A new adsorption gel has been developed by immobilizing N-aminoguanidine (AG), a chelating ligand, on persimmon tannin extract through consecutive reactions. Adsorption behavior of the gel was investigated for the adsorptive separation and recovery of precious metal ions from varying concentration of HCl medium. The adsorption isotherms of precious metal ions on the gel were described by the typical monolayer type of Langmuir model and the maximum adsorption capacities were evaluated as 8.90 mol kg(-1) for Au(III), 2.01 mol kg(-1) for Pd(II) and 1.01 mol kg(-1) for Pt(IV). Real time applicability of the gel was examined for the recovery of precious metals from actual leach liquor of e-waste leached with chlorine containing hydrochloric acid. The gel was found to be highly efficient and selective for the uptake of targeted metal ions in the presence of excess base metal ions and also exhibited superior selectivity over commercially available anion exchange resins.

Optimization of an adsorption process for tetrafluoroborate removal by zirconium (IV)-loaded orange waste gel from aqueous solution.

This investigation provides new insights into the effective removal of tetrafluoroborate (BF4-) by means of bio-sorption on waste generated in the orange juice industry. It was undertaken to evaluate the feasibility of zirconium (IV)-loaded saponified orange waste gel for BF4- removal from an aqueous solution. Batch adsorption experiments were carried out to study the influence of various factors such as pH, presence of competing anions, contact time, initial BF4- concentration and temperature on the adsorption of BF4-. The optimum BF4- removal was observed in the equilibrium pH region 2-3. The presence of coexisting anions showed no adverse effect on BF4- removal except SO4(2-). The equilibrium data at different temperatures were reasonably interpreted by the Langmuir adsorption isotherm and the maximum adsorption capacities were evaluated as 2.65, 3.28, 3.87 and 4.77 mmol g(-1) at 293, 298, 303 and 313 K, respectively. Thermodynamic parameters such as deltaGo, deltaHo and deltaSo indicated that the nature of BF4- adsorption is spontaneous and endothermic. The results obtained from this study demonstrate the potential usability of orange waste after juicing as a good BF4- selective adsorbent.

Adsorptive removal of fluoride from aqueous solution using orange waste loaded with multi-valent metal ions.

Adsorption gels for fluoride ion were prepared from orange waste by saponification followed by metal loading. The pectin compounds contained in orange waste creates ligand exchange sites once it is loaded with multi-valent metal ions such as Al(3+), La(3+), Ce(3+), Ti(4+), Sn(4+), and V(4+) to be used for fluoride removal from aqueous solution. The optimum pH for fluoride removal depends on the type of loaded metal ions. The isotherm experiments showed the Langmuir type monolayer adsorption. Among all kinds of metal loaded gels tested, Al loaded gel appeared to exhibit the most favorable adsorption behavior. The adsorption kinetics of fluoride on loaded gel demonstrated fast adsorption process. The presence of NO(3)(-), Cl(-) and Na(+) ions has negligible effect on fluoride removal whereas SO(4)(2-) and HCO(3)(-) retarded the fluoride removal capacity in some extent. Fluoride removal at different adsorbent doses showed that fluoride concentration can be successfully lowered down to the acceptable level of environmental standard. The fluoride adsorption mechanism was interpreted in terms of ligand exchange mechanism. The complete elution of adsorbed fluoride from the gel was successfully achieved using NaOH solution.

Adsorption behavior of heavy metals onto chemically modified sugarcane bagasse.

A new process for the xanthation of sugarcane (Saccharum officinarum) bagasse was investigated for the separation of cadmium, lead, nickel, zinc and copper from their aqueous solutions. Adsorption capacity of the charred xanthated sugarcane bagasse (CXSB) was found to be significantly more than the several biosorbents reported in the literatures. The modified material was characterized by FTIR and elemental analysis. The kinetics of sorption of the tested metals was fast, reaching equilibrium within 20-40 min. The maximum adsorption capacities evaluated in terms of mol/kg dry gel were 1.95 for Cd(II), 1.58 for Pb(II), 2.52 for Ni(II), 2.40 for Zn(II) and 2.91 for Cu(II), respectively. The high adsorption capacity and the kinetics results indicated that CXSB can be used as the selective adsorbent for the removal of these respective metal ions from wastewater.

Effective removal and recovery of antimony using metal-loaded saponified orange waste.

Zr(IV) and Fe(III) ions were loaded onto an orange waste precursor to prepare a metal-loaded orange waste gel, which was investigated for the adsorptive removal and recovery of antimony (III and V) from an aqueous environment. The loading capacity of the orange waste for Zr(IV) and Fe(III) was found to be 1.40 and 1.87 mmol/g, respectively. The maximum batch mode sorption capacity of the Zr(III)-loaded saponified orange waste (SOW) gel was found to be 0.94 mmol/g for Sb(III) and 1.19 mmol/g for Sb(V). A nearly similar result was found for the Fe(III)-loaded SOW gel with the sorption capacity for Sb(III) and Sb(V) being 1.12 and 1.19 mmol/g, respectively. The presence of a variety of anionic species such as carbonate, chloride, nitrate and sulfate had no influence on the adsorption of both Sb(III) and Sb(V). A column adsorption-elution test demonstrated the utility of this system in continuous mode. Selective sulfide precipitation of antimony is one of the major findings in the present work, which clearly suggests a means of effective recovery of antimony from solution containing antimony and other metal ions. Due to their low cost, availability and significantly high adsorption capacity, the metal-loaded gels are expected to be effectively employed for the removal and recovery of antimony from aqueous solution, thus leading to the establishment of a greener environment.

Selective recovery of precious metals by persimmon waste chemically modified with dimethylamine.

Persimmon waste was chemically modified with dimethylamine (DMA) to obtain a tertiary-amine-type gel, named DMA persimmon waste gel (DMA-PW). It was found to be effective for the adsorption of Au(III), Pd(II), and Pt(IV) in hydrochloric acid medium. In contrast, base metals such as Cu(II), Zn(II), Fe(III), and Ni(II) were not practically adsorbed. The formation of ion pairs of the metal chloro complex anions with the protonated adsorption gels was proposed as the main adsorption process. The gel exhibited selectivity only for precious metals with a remarkably high capacity for Au(III), i.e., 5.63 mol/kg dry gel and comparable capacities, i.e., 0.42 and 0.28 mol/kg for Pd(II) and Pt(IV), respectively. According to the kinetic and electrochemical studies, the adsorption rate of Au(III) was greatly enhanced by the chemical modification. Also, its excellent adsorption characteristics for the precious metals were confirmed by adsorption and elution tests using a column packed with the DMA-PW gel.

Chemical modification of carbonized wheat and barley straw using HNO3 and the adsorption of Cr(III).

The effects of oxidation using HNO(3) on the properties of the carbonized wheat and barley straw were investigated by measuring different properties such as specific surface area, PZC, total surface acidic groups as well as FTIR and TG-DTA. A small decrease in the specific surface area due to pore blockage was observed after oxidation. After oxidation, the acidity was increased considerably and the point of zero charge shifted from approximately pH 9 to pH 2 in both types of carbon. By the oxidation of the carbon with nitric acid, carboxylic groups were produced as shown by absorption peaks at 1750 cm(-1) in the FTIR spectra. Boehm titration results showed that the number of carboxyl groups increased by approximately 11-fold after oxidation. The oxidized carbon samples were compared with the unoxidized original carbon samples for Cr(III) adsorption. It was observed that the oxidized carbons exhibit high adsorption efficiencies for Cr(III) ions compared to the original carbonized straws and this can be correlated to the decrease in PZC which is mainly due to the increase in carboxylic functional groups in the oxidized carbonized straws and these are responsible for their cation ion exchange phenomenon.

Dynamic rejection of colloidal particles with generating dextran by enzymatic reaction.

Dextransucrase forms a complex with dextran during an enzymatic reaction with sucrose. Using its enzymatic character, we performed a continuous and dynamic rejection of colloidal particles by generating dextran with dextransucrase immobilized in an inorganic porous membrane. Inorganic membranes having 1.9 and 3.0 U/g of immobilized dextransucrase, and 4.1 and 9.4 mg/g of generated dextran, respectively, had constant rejection percentages for 55 and 100 nm colloidal particles in permeating solutions. On the other hand, permeating sucrose solutions containing colloidal particles through a dextran-immobilized membrane dynamically increased the rejection percentages of the colloidal particles owing to dextran generation via enzymatic reaction. The dynamic increase was due to the gradually generating dextran dynamically occupying the membrane pore with its steric volume.

Leaching of phosphorus from incinerated sewage sludge ash by means of acid extraction followed by adsorption on orange waste gel.

Ashes from sewage sludge incineration have a high phosphorus content, approximately 8% (W/W), which indicates a potential resource of the limiting nutrient. Incineration of sewage sludge with subsequent recovery of phosphorus is a relatively new sludge treatment technique. In this article, the leaching of phosphorus by using sulfuric acid as well as hydrochloric acid by means of several batch experiments was presented. At the same time a selective recovery of phosphorus by adsorption was also discussed. The effects of acid concentration, temperature and time on extraction were studied. The phosphorus leaching increased with the increase in acid concentration and temperature. Kinetic studies showed that the complete leaching of phosphorus took place in less than 4 h. Selective adsorption of phosphorus by using orange waste gel provided a hint for recovery of this natural resource, which eventually could meet the ever-increasing requirement for phosphorus. The overall results indicated that the incinerated sewage sludge ash can be treated with acid to efficiently recover phosphorus and thus can be considered a potentially renewable source of phosphorus.

Grape waste as a biosorbent for removing Cr(VI) from aqueous solution.

Grape waste generated in wine production is a cellulosic material rich in polyphenolic compounds which exhibits a high affinity for heavy metal ions. An adsorption gel was prepared from grape waste by cross-linking with concentrated sulfuric acid. It was characterized and utilized for the removal of Cr(VI) from synthetic aqueous solution. Adsorption tests were conducted in batch mode to study the effects of pH, contact time and adsorption isotherm of Cr(VI), which followed the Langmuir type adsorption and exhibited a maximum loading capacity of 1.91 mol/kg at pH 4. The adsorption of different metal ions like Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at different pH values 1-5 has also been investigated. The cross-linked grape waste gel was found to selectively adsorb Cr(VI) over other metal ions tested. The results suggest that cross-linked grape waste gel has high possibility to be used as effective adsorbent for Cr(VI) removal.

Chestnut pellicle for the recovery of gold.

Recovery of Au(III) from hydrochloric acid medium by using crosslinked chestnut pellicle (CCP) gel was studied. Strong selectivity was observed for Au(III) showing negligible affinity for other precious metals and some base metal ions tested. The adsorption isotherm study exhibited the maximum loading capacity of the gel as high as 10.6 mol or about 2.1 kg gold per kg dry weight of gel. The reduction of Au(III) ion to elemental form during adsorption process is expected to be the reason of high selectivity and high capacity for Au(III). Kinetic studies at various temperatures confirm an endothermic adsorption process following the pseudo-first order rate law.

Novel carbonyl-group-containing dextran synthesis by pyranose-2-oxidase and dextransucrase.

The carbonyl polysaccharide, keto-dextran, was synthesized by the regioselective oxidation of sucrose and by the subsequent transfer reaction of the oxidized sucrose. The regioselective oxidation of sucrose was performed by bioconversion with pyranose-2-oxidase (EC 1.1.3.10). After 24h, the conversion percentage of sucrose into keto-sucrose was 100% as determined by a colorimetric method with dinitrophenylhydrazine. Converted keto-sucrose was polymerized to keto-dextran by dextransucrase (EC 2.4.1.5). Polymerization of keto-dextran was confirmed by the increase in molecular weight and amount of keto-dextran produced. The amount of keto-dextran produced decreased to 80% of the amount of dextran produced owing to the substrate recognition of DSase. From a Lineweaver-Burk reciprocal plot, the Michaelis constants for sucrose and keto-sucrose were 4.6 mmol L(-1) and 14.0 mmol L(-1), respectively. The keto-dextran had a carbonyl group in all glucose units.

Dimethylamine-modified waste paper for the recovery of precious metals.

Waste newsprint paper was modified with dimethylamine (DMA) to obtain a tertiary amine type adsorption gel called DMA-paper gel. This new derivative was investigated for adsorption, from hydrochloric acid medium, of gold, palladium, and platinum as well as some base metals. The gel exhibited selectivity only for precious metals with a remarkably high capacity for Au(III), i.e., 4.6 mol/kg dry gel and comparable capacities, i.e., 2.1 and 0.9 mol/kg for Pd(II) and Pt(IV), respectively. Also, Au(III) was reduced to the elemental form during adsorption. Furthermore, column adsorption and subsequent elution of the adsorbed metal ions by acidic thiourea revealed encouraging recoveries (approximately 90%), thus enhancing the scope of the gel for effective preconcentration, separation, and recovery of precious metals. The effectiveness of recovery of precious metals from real industrial liquor was also tested, and it showed highly encouraging results with respect to the stability of the gel in the harsh medium, and selectivity for the targeted metal ions in the presence of excess of other metal ions.

Removal and recovery of phosphorus from water by means of adsorption onto orange waste gel loaded with zirconium.

Orange waste, an available biomass, was immobilized with zirconium(IV) to investigate its feasibility for phosphate removal from an aquatic environment. Kinetics, effects of pH and foreign anions, and the adsorption isotherm for phosphate have been examined. The adsorption capacity has been compared to that of two commercially available adsorbents such as zirconium ferrite and MUROMAC XMC 3614. The prepared gel was an effective adsorption gel for phosphate removal with a reasonably high sorption capacity of 57mg-P/g, which was four times higher than that of zirconium ferrite. The highest removal of phosphate was observed at low pH, whereas higher pH suppressed phosphate removal, but even up to pH 9 more than 85% phosphate removal was observed. Adsorbed phosphate was eluted by NaOH solution. Fixed bed column-mode experiments confirmed the complete adsorption of phosphate in continuous-mode operation. Throughout the operating conditions, zirconium was not leaked.

Pre-concentration and separation of heavy metal ions by chemically modified waste paper gel.

Iminodiacetic acid was immobilized on waste paper by chemical modification in order to develop a new type of adsorption gel for heavy metal ions. Adsorption behavior of the gel was investigated for a number of metal ions, specifically Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. From batch adsorption tests, the order of selectivity was found to be as follows: Cu(II)>>Fe(III)>Pb(II)>Ni(II)>>Co(II)>Cd(II). Column tests were carried out for pairs of metal ions to understand the separation and pre-concentration behavior of the gel. It was found that mutual separation of Ni(II) from Co(II) and that of Pb(II) from Cd(II) can be achieved at pH 3. Similarly, selective separation of Cu(II) from Cu(II)-Fe(III) and Cu(II)-Pb(II) mixtures at pH 1.5 and 2, respectively, was observed by using this new adsorption gel. In all cases, almost complete recovery of the adsorbed metal was confirmed by elution tests with HCl.