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The removal of Cr(VI) from the water was studied using raw and modified banana peels and pseudostem wastes as bio-adsorbent under the batch adsorption technique at room temperature. The chemical modification of raw adsorbents was performed by treating them with concentrated sulphuric acid. Characterizations were performed by FTIR, XRD, and SEM analyses. The raw form of adsorbents showed insignificant adsorption compared to the charred form. Therefore, the further process was carried out using modified adsorbents only. The maximum adsorption capacity for charred banana peel (CBP) and charred banana pseudostem (CBS)was found to be maximum at optimum equilibrium pH 2. The adsorption data fitted well with the Langmuir adsorption model and followed pseudo-second-order kinetics. Therefore, owing to high efficiency and low cost with maximum removal percentage, thus prepared adsorbents are expected to be used satisfactorily in the adsorption of Cr(VI) from aqueous solutions.

Hydrated tri metal oxide (HTMO) precipitate is investigated using a mixed solution containing cerium, aluminum, and titanium by precipitation for fluoride ion removal from water. PZC for the investigated HTMO precipitate is determined to be 6.5 from pH drift method. Fluoride adsorption by HTMO precipitate is pH dependent, with adsorption rates of more than 98 percent occurring at pH 2.3 to 6.7. The highest solid phase distribution of fluoride is observed at pH around 6. Fluoride adsorption onto HTMO precipitate increased with temperature, implying that the adsorption reaction is endothermic, as evidenced by the positive value of ∆H⁰ calculated from the thermodynamic calculations. The spontaneous process is indicated by a negative ∆G⁰ value for all temperatures. The fluoride adsorption rate onto this adsorbent is rapid, and equilibrium is reached in less than four hours. An alkali (NaOH) solution effectively desorbed fluoride from a fluoride-loaded HTMO precipitate. As a result, the HTMO precipitate studied in this work is expected to be a viable as fluoride-removing material from water.

The present study reports the fluoride uptake potential of Zr(IV)-loaded saponified banana peels (Zr(IV)-SBP) from water. Zr(IV)-SBP was synthesized by loading Zr(IV) onto banana peel biomass after saponification and sorbent characterization was performed by using different techniques including FE-SEM (Field Emission Scanning Electron Microscopy), FTIR (Fourier Transform Infra-Red) spectroscopy and zeta potential analysis. Batch experiments were carried out to examine the monitoring factors for the uptake of fluoride onto the investigated adsorbent. The optimal pH and contact time were found to be 2.94 and 300 minutes, respectively. The results from characterization techniques concurred that Zr(IV)-SBP have prominent adsorption sites favorable for the sorption of fluoride ions. The sorption behavior of fluoride onto Zr(IV)-SBP was best fitted with the Langmuir adsorption isotherm and pseudo-second-order kinetics model. The maximum adsorption capacity of Zr(IV)-SBP was 36.02 mg/g using the Langmuir isotherm model. The coexisting ions like chloride and nitrate caused very small interference, elevated concentration of sulphate notably lowers the fluoride adsorption percentage in the binary system, and the sorption using multiple systems was lowered significantly which is due to the synergistic effect of co-existing interfering ion. The adsorbed fluoride was completely desorbed using 2M NaOH solution. Fluoride sorption performance of Zr(IV)-SBP demonstrated that it can be a low cost, environmentally benign and one of the highly potent alternatives for the remediation of fluoride ions to avoid ablation on the water.

A novel biosorbent for the sequestration of phosphate from the water was explored by loading Zr(IV) onto saponified watermelon rind (SWR). SEM, FT-IR and EDX were carried out for the structural cha...

The main target of this study was to evaluate the efficiency of charred xanthated sugarcane bagasse (CXSB) and charred sugarcane bagasse (CSB) in the removal of Hg(ii) ions from aqueous media. Batch experiments were performed to study the experimental parameters such as effects of pH, concentration, contact time and temperature. The adsorption velocity of Hg(ii) onto CSB and CXSB was fast and reached equilibrium within 60 minutes. Isotherm and kinetic studies showed that Hg(ii) uptake using both the biosorbents followed Langmuir isotherm and pseudo second order kinetics. The maximum adsorption capacity of Hg(ii) at optimum pH 4.5 onto CSB and CXSB was found to be 125 mg g

Various separation techniques have been successful for the removal of fluoride from aqueous solution. In this review, an extensive list of various biomass-based adsorbents from literature has been explored and their adsorption capacities under different conditions for the removal of fluoride available in the literature to date are presented. Several adsorbents have shown good adsorption capacities; however, modified biomass had shown excellent adsorption capacities compared to commercial materials. This paper reviews the fluoride uptake capacities of biomass materials and their modified forms as adsorbents against different experimental limits.

There is a growing research interest in the development of adsorbents based on agricultural wastes (AWs) for the removal of phosphate from waste water sources, which otherwise can cause eutrophication. Nevertheless, due to the lack of active exposed surface sites, raw AWs-based adsorbents are usually inefficient for the adsorption of phosphate from aquatic environment. Consequently, modification of raw adsorbents has been frequently used to improve their phosphate adsorption capacity. Of the various methods of modification, this review paper focused on most widely used chemical modification method. It presents a critical and comprehensive review of the literature on the effectiveness of metal-loaded agricultural wastes (MLAWs)-based adsorbents in removing and recovering of phosphate from waste waters. Mechanisms and factors affecting phosphate adsorption as well as phosphate desorption and regeneration from MLAW adsorbents are critically evaluates. If phosphate from waste waters can be of economical value, regeneration may partly overcome the future shortage of global phosphate rock reserves. It is evident from the literature survey presented herein that MLAWs-based adsorbents exhibited as potential adsorbent for the removal/recovery of phosphate from waste waters. However, there still needs a refined practical utility of these adsorbents on a commercial scale, which may serve as the novel, cost effective and environmentally benign methods of modification.

A novel type of adsorbent, TiO2 impregnated pomegranate peels (PP@TiO2) was successfully synthesized and its efficacy was investigated based on the removal of As(III) from water. The adsorbent was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometer (EDS), X-ray Diffraction (XRD) analysis, and Fourier Transform Infrared (FTIR) Spectroscopy, to evaluate its morphology, elemental analysis, crystallinity, and functional groups, respectively. Batch experiments were conducted on PP@TiO2 for As(III) adsorption to assess the adsorption isotherm, effect of pH, and adsorption kinetics. Characterization data suggested that TiO2 was successfully impregnated on the biomass substrate. The equilibrium data better fitted to the Langmuir isotherm model having a maximum adsorption capacity of 76.92 mg/g and better distribution coefficients (KD) in the order of ~103 mL/g. The highest percentage of adsorption was found at neutral pH. The adsorption kinetics followed the pseudo-2nd-order model. X-ray Photoelectron Spectroscopy (XPS) of the adsorption product exhibited that arsenic was present as As(III) and partially oxidized to As(V). PP@TiO2 can work effectively in the presence of coexisting anions and could be regenerated and reused. Overall, these findings suggested that the as-prepared PP@TiO2 could provide a better and efficient alternative for the synergistic removal of As(III) from water.

We have synthesized zirconium-modified pomegranate peel (SPP@Zr) as a novel biomass-based anion exchanger for the effective remediation of arsenate (As(V)) from contaminated water. The synthesized material was morphologically and texturally characterized. The adsorption kinetics and isotherm studies revealed that the experimental results could be better interpreted in terms of pseudo-second-order kinetic and Langmuir isotherm models, respectively. The SPP@Zr exhibited outstanding remediation capacities for As(V), having a maximal loading capacity of 83.33 mg g−1 at pH 4.0 and 298 K. Thermodynamic studies revealed the arsenate sorption onto as-synthesized adsorbent was endothermic and spontaneous. The spent adsorbent could be readily regenerated using an alkaline solution and be repeatedly used. The mechanism study has shown that both ligand exchange and electrostatic attraction play crucial roles in the adsorption of oxyanions of As(V). An X-ray photoelectron spectroscopy (XPS) study of sorption products revealed that no reduction of As(V) to As(III) occurred during the adsorption process. Finally, the SPP@Zr was applied for the dearsenification of natural groundwater samples and was found very efficient at capturing arsenic far below the mark of tolerance level (10 μg L−1) of drinking water.

Adsorptive removal of arsenic using adsorption gels prepared from orange and apple juice residues was reviewed by summarizing the authors’ previous papers. Orange and apple juice residues contain a large amount of pectin, partly methyl-esterified pectic acid, which exhibits high affinity for high-valent metal ions such as iron(III), rare earths(III) and zirconium(IV). Anionic species of arsenic(III, V) are effectively and selectively adsorbed on pectic acid gel via loading these high-valent metal ions. Raw orange juice residue was saponified using calcium hydroxide to improve the loading capacity for these metal ions. It was found that zirconium(IV) exhibits the most suitable adsorption behaviors for arsenic(III, V). Similar result was obtained also for apple juice residue. An actual sample of acid mine drainage from the Horobetsu mine which contained a high concentration of iron and low concentration of arsenic, was tested using the adsorption gel prepared from orange juice residue and the results were compared with those from the current treatment process based on coprecipitation with iron hydroxide. The new process using the above- mentioned adsorption gel was proposed for treatment of such acid mine drainage.

In this study adsorptive removal of Pb(II) and Cu(II) from aqueous solution by using environmental friendly natural polymers present in exhausted tea leaves has been studied. The biosorbent was modified with dimethylamine to introduce N-functional groups on the surface of adsorbent. The modified adsorbent was characterized by elemental analysis, zeta potential analysis, SEM, DRFTIR, XRD and TG/DTA analysis to conform the modification. Adsorption capacity of the adsorbent was determined as the function of pH of the solution, initial concentration of the solution and contact time. The adsorption experiments were performed using batch experiments. The maximum adsorption capacities of the adsorbent were found to be 91.68 and 71.20 mg/g for Pb(II) and Cu(II), respectively. To minimize the process cost, regeneration of the biosorbent and recovery of metal ions was explored by desorption study. The results indicate that the adsorbent holds great potential for the sequestration of Pb(II) and Cu(II) from their aqueous solution. Hence the modified exhausted tea leaves (MTL) have been investigated as a new cost effective and efficient biosorbent for removal of Pb(II) and Cu(II) from their aqueous solution.

Chemically modified adsorbent based on Phragmities stem has been investigated by treating with concentrated sulfuric acid at 2:1 weight/volume ratio. The maximum loading capacity for Al(III) and Fe(II) onto phosphorylated charred Phragmities waste PCPW adsorbent was found to be 148 mg/g and 200 mg/g, while for Cr(VI) 200 mg/g, respectively, at their optimal pH. Similarly, it was 166.66 mg/g and 90.90mg/g for Al(III) and Fe(II) onto the charred Phragmities waste CPW, respectively. The adsorption process followed the Freundlich isotherm and pseudo-second order kinetic models. The desorption of the loaded metal ions recovery was found to be to the extent of 82%, 91% and 100% for Al(III), Fe(II) and Cr(VI), respectively.Journal of Institute of Science and Technology, 2015, 20(2): 145-152

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.

Adsorbent for strontium (Sr2+) ion removal was prepared from orange waste generated in an orange juice factory. The orange juice residue (OJR) was treated with lime water to prepare saponified orange juice residue (SOJR). The energy dispersive X-ray (EDX) spectroscopic analysis revealed that substitution of Ca2+ ions in SOJR by Sr2+ ions takes place during the adsorption process. The adsorption of Sr2+ ions onto SOJR was fast and strongly pH dependent. Maximum adsorption occurred at pH higher than 5. The adsorption isotherm study showed maximum adsorption capacity of SOJR for Sr2+ ion was 833.4 mmol/kg. Equimolar amount of Ca2+ was found to be released from SOJR during Sr2+ adsorption also indicating that adsorption of Sr2+ on SOJR takes place according to the Ca2+ substitution reaction by cation exchange mechanism. Thus, the adsorption gel prepared in this study can be a promising adsorbent to remove Sr2+ from aqueous solution.

An efficient and cost effective bioadsorbent has been prepared from exhausted tea leaves using hydrazine monohydrate. The aminated tea leaves (ATL) was characterised by elemental and spectral analysis. The batch adsorption study was performed using ATL for the removal of Pb ++ and Zn ++ from their aqueous solution. Adsorption experiment was conducted as the function of solution pH, initial metal concentration and contact time. The maximum adsorption capacity of the adsorbent was found to be 120.8 mg/g for Pb ++ and 79.76 mg/g for Zn ++ . These results indicated that the aminated tea leaves hold great potential to remove Pb ++ and Zn ++ from aqueous solution. DOI: http://dx.doi.org/10.3126/jncs.v30i0.9383 Journal of Nepal Chemical Society Vol. 30, 2012 Page: 123-129 Uploaded date : 12/20/2013

Different types of agricultural waste materials have been explored for their efficiency in removing heavy metal ions from aqueous solution. A biomass of Desmostachya bipinnata (DB) was investigated as the potential bio-adsorbent for the removal of Cd (II)) and Cu (II) from wastewater. The surface of DB was chemically grafted with ethylenediamine. It was characterized by elemental, FTIR and SEM analysis. The maximum adsorption capacity of MDB in the removal of Cd (II) and Cu (II) were 30.4mg/g and 41.6 mg/g at their optimum pH 6 and 5, respectively. The experimental data followed the Langmuir isotherm and pseudo-second order kinetic model The research results indicated that D. bipinnata can be an alternative, efficient and ecofriendly material for the removal of Cd (II) and Cu (II) from wastewater.DOI: http://dx.doi.org/10.3126/jncs.v30i0.9333Journal of Nepal Chemical Society Vol. 30, 2012 Page: 37-44 Uploaded date: 12/16/2013

A novel process for cadmium recovery from mid gut of scallops is investigated based on the systematic information of the process system. Adsorption of cadmium was accompanied according to the cation exchange mechanism and the equilibrium pH increased to around 7 due to the isomorphous substitution of cadmium with that calcium of SAJR. A complete recovery of cadmium has been achieved from the process that we have developed from this study. DOI: http://dx.doi.org/10.3126/jncs.v30i0.9337 Journal of Nepal Chemical Society Vol. 30, 2012 Page: 62-65 Uploaded date : 12/16/2013

An effective chemically modified adsorbent based on sugarcane waste has been prepared by treating with concentrated sulphuric acid in 2:1weight/volume ratio. Thus prepared adsorbent has been found to be effective in the adsorption of chromium from aqueous medium. The efficacy of the adsorbent in the removal of chromium was evaluated by batch adsorption method. The effect of initial concentration, contact time and pH of the solution was investigated. The maximum adsorption capacity onto this adsorbent was found to be 195 mg/g at their optimal pH 1 at which unmodified bagasse has only 58 mg/g. The characterization of adsorbent was done by determining surface area and Boehm’s titration method. Freundlich isotherm and pseudo-second order kinetic model gave better explanation of the adsorption process.

In a shallow pond at Biratnagar, Nepal, importance value index of T. domingensis ranged between 134 (September) and 179 (May), and net primary productivity of the plant along with associated species was 1001.23 g/m2/yr. Maximum concentrations of nitrogen (2.76%) and potassium (2.87%) occurred in leaves, and phosphorus (0.95%) in roots of the plant in January, and three month old air-dried seeds of the plant had optimum germination (84%) under red light on moist filter papers. The pond water had minimum values of pH (6.12), turbidity (51.2 NTU), conductivity (5.39 ds/m), total dissolved solids (75.5 mg/l, nitrate and nitrite (0.01 mg/l) and potassium (5.6 mg/l) in September; total nitrogen (1.01 mg/l) in May; and ammonia (0.26 mg/l) and total phosphorus (0.72 mg/l) in January. The sediment (mud) of the pond was silty-sandy loam with annual averages of pH 6.6, nitrogen 0.23%, phosphorus 0.006%, potassium 0.04%, organic carbon 4.05% and C/N ratio 17.6:1.

An efficient and cost effective non-conventional biosorbent has been prepared from tea waste by amination with ethylenediamine. The prepared adsorbent, ATW was characterized using elemental analysis, scanning electron microscopic image and FTIR spectroscopy. Its adsorption behavior for Cu ++ and Zn ++ ions was studied by using batch adsorption method. The maximum adsorption capacity onto ATW was found to be 46.4mg/g and 30.08 mg/g for Cu ++ and Zn ++ respectively. The effect of pH of solution, initial metal concentration and contact time for removal of metal ions were studied. The applicability of data was analyzed by Langmuir isotherm. The kinetics of removal of Cu ++ and Zn ++ ions was studied using pseudosecond order model, in which the data were well fitted. DOI: http://dx.doi.org/10.3126/jncs.v28i0.8058 Journal of Nepal Chemical Society Vol.28, 2011 Page 48-53 Uploaded date : May 7, 2013

Dried orange juice residue (DOJR) marketed as cattle food in Japan was converted into a promising adsorbent for fluoride as a result of chemical loading with Zr(IV), Ce(IV) and Al(III). The effectiveness of the metal loaded DOJR in adsorbing trace fluoride concentrations from synthetic and actual waste water were investigated. Energy dispersive X-ray (EDX) and infra red (IR) spectroscopic analysis confirmed the effective adsorption of Zr(IV) ions on DOJR in addition to fluoride ion on Zr(IV)-loaded DOJR. The amount of Zr(IV), Ce(IV) and Al(III) loaded on the DOJR were evaluated as 0.90, 0.85 and 0.97 mmol/g, respectively, while the maximum adsorption capacity of fluoride on the Zr(IV), Ce(IV) and Al(III) loaded DOJR were evaluated as 1.43, 1.22 and 0.67 mmol/g, respectively. Application of Zr(IV) loaded DOJR using actual waste plating solutions exhibited effective removal of trace concentration of fluoride to acceptable level. The negligible interference of coexisting anions such as nitrates, carbonates and chlorides makes the Zr(IV) loaded DOJR a promising sorbent for waste water treatment. The adsorbed fluoride was effectively desorbed using an alkali (NaOH) solution for its regeneration. Thus, this work shed light on the potential application of metal loaded DOJR to remediate aquatic environment polluted with fluoride.

In the present work an efficient and cost-effective biosorbent was prepared by chemical modification of tealeaves. Amine-functional group was introduced on the surface of adsorbent using dimethylamine. The adsorbent was characterized by SEM, FTIR and elemental analysis. The adsorption capacity of the adsorbent for Cd (II) was determined as the function of pH of the solution, concentration of metal ions and contact time. The maximum adsorption was found to be 77 mg/g at pH 6. Nepal Journal of Science and Technology Vol. 13, No. 2 (2012) 109-114 DOI: http://dx.doi.org/10.3126/njst.v13i2.7722

The biomass of Desmostachy bipannata (Kush, a religious plant of Hindus) was modified for the better adsorption of metal ions from aqueous solution. The FTIR and SEM images were used for the characterization of biomass. The adsorptive separation of metal ions from aqueous solution was studied with equilibrium isotherm and kinetic model. Langmuir adsorption isotherm and pseudo second order kinetic model showed better explanation for the adsorption process. The experimental results suggest that biomass from Kush can be used as an effective biosorbent for the removal of metal ions from aqueous solution. Nepal Journal of Science and Technology Vol. 13, No. 1 (2012) 101-106 DOI: http://dx.doi.org/10.3126/njst.v13i1.7448

The industrial discharge of heavy metals into waters' course is one of the major pollution problems affecting water quality. Therefore, they must be removed prior to their discharge into waste streams. An efficient and low-cost bioadsorbent has been investigated from Desmostachya bipinnata (Kush) by charring with concentrated sulphuric acid and functionalized with dimethylamine.It was characterised by SEM, FTIR and elemental analysis. The effect of pH, initial concentration and contact time of the metal solution was monitered by batch method. The maximum adsorption capacities were determined for Cd and Zn at their optimum pH 6. The equilibrium data were analysed using Langmuir and Freundlich isotherm models. Langmuir isotherm model fitted well and the rate of adsorption followed the pseudo second order kinetic equation.DOI: http://dx.doi.org/10.3126/jncs.v27i1.6669 J. Nepal Chem. Soc., Vol. 27, 2011 107-114

Removal of fluoride is investigated onto several metal ions loaded phosphorylated orange juice residue and commercially available alumina. The experimental results revealed that cerium (IV) loaded phosphorylated orange waste indicated excellent fluoride removal efficiency at acidic pH range and while that lanthanum loaded at neutral pH range. Both the metal loaded adsorbents are found superior to the commercially available activated alumina.DOI: http://dx.doi.org/10.3126/jncs.v27i1.6660 J. Nepal Chem. Soc., Vol. 27, 2011 61-66

A new type of adsorbent for rare earth metal ions was prepared from orange waste by simple method of saponification reaction with lime water. Adsorption test of rare earth metals ions such as Sm(III), Ho(III), La(III), Sc(III) and Lu(III) suggested that these rare earth metals ions were effectively adsorbed on this adsorbent. Adsorption of fluoride ion was investigated using this adsorbent after being loaded with above-mentioned rare earth metal ions. It was found that fluoride adsorption was fast and dependent on solution pH. The maximum adsorption capacity for fluoride was evaluated as 0.60, 0.92, 1.06 and 1.22 mmol/g for Sc(III), Ho(III), La(III) and Sm(III) loaded adsorbent, respectively. Fluoride ions were successfully removed below the environmental standard by the use of small amount of La(III) loaded adsorbent. Adsorbed fluoride was successfully eluted by using NaOH solution.

Introduction of xanthate group onto sugarcane (Saccharum officinarum) bagasse has been investigated for the removal of cadmium, lead, nickel, zinc, and copper from their aqueous media. The charred xanthated sugarcane bagasse (CXSB) was found to have significant adsorption capacity which is more than that of various bio-sorbents mentioned in the available literatures. The newly developed bio-sorbent was characterized by SEM, FTIR, TGA/DTA, and elemental analysis. The velocity of sorption of the tested metals was fast, reaching equilibrium within 40 min. The maximum loading capacities was found to be 225 for Cd(II), 318 for Pb(II), 144 for Ni(II), 164 for Zn(II), and 178 for Cu(II) mg g−1, respectively. The fast kinetics results and high adsorption capacity indicated that CXSB can be applied as the selective adsorbent for the treatment of heavy metal ions from aqueous solutions.

Orange waste, produced during juicing has been loaded with zirconium(IV) so as to examine its adsorption behavior for both As(V) and As(III) from an aquatic environment. Immobilization of zirconium onto the orange waste creates a very good adsorbent for arsenic. Adsorption kinetics of As(V) at different concentrations are well described in terms of pseudo-second-order rate equation with respect to adsorption capacity and correlation coefficients. Arsenate was strongly adsorbed in the pH range from 2 to 6, while arsenite was strongly adsorbed between pH 9 and 10. Moreover, equimolar (0.27 mM) addition of other anionic species such as chloride, carbonate, and sulfate had no influence on the adsorption of arsenate and arsenite. The maximum adsorption capacity of the Zr(IV)-loaded SOW gel was evaluated as 88 mg/g and 130 mg/g for As(V) and As(III), respectively. Column adsorption tests suggested that complete removal of arsenic was achievable at up to 120 Bed Volumes (BV) for As(V) and 8 0BV for As(III). Elution of both arsenate and arsenite was accomplished using 1 M NaOH without any leakage of the loaded zirconium. Thus this efficient and abundant bio-waste could be successfully employed for the remediation of an aquatic environment polluted with arsenic.

Orange waste has been chemically modified and loaded with lanthanum(III) and/or cerium(III) to examine its adsorption behavior to both As(V) and As(III). Arsenate removal was found to be favored over a pH range of 6 ∼ 9.5 while arsenite removal took place at pH values ranging from 9 to 11. The maximum sorption capacity of the gel for As(III) removal was evaluated as 43 mg/g, while that for As(V) was 42 mg/g. Column-mode tests using the La(III)-loaded gel confirmed a complete removal of As(V). A reasonably high adsorption potential within the design criteria makes the present gel an alternative choice for arsenic removal.

A highly selective and efficient biosorbent has been prepared from orange waste by introducing a phosphoric group at its polymer analog by simple chemical modification. Their adsorption behavior for several kinds of metal ions was studied and it was found to exhibit excellent selectivity towards several metal ions. As a typical example, a binary mixture of In(III) and Zn(II) was studied by using a packed column, indicating that In(III) ion can be selectively separated from its mixture with a concentration factor of 63 times. The maximum adsorption capacities evaluated in terms of mol/kg dry gel were 0.70 for In(III) and Ga(III), 0.97 for Cu(II), 1.15 for Pb(II) and Zr(IV), and 3.06 for Fe(III), respectively.

From two kinds of seaweeds, Porphyra yezoensis and Ulva japonica, adsorption gels for heavy metal ions were prepared by enhancing their adsorptive properties and diminishing the aqueous solubility. An environmental benign crosslinking using calcium have shown maximum adsorption capacity of 0.67 mol/kg dry gel for lead(II), which is slightly lower as compared to the adsorbents crosslinked with synthetic crosslinking agent (0.76 mol/kg). Fixed bed column studies for a binary mixture containing lead(II) and zinc(II) revealed that lead(II) can be mutually separated from zinc(II) with a concentration factor of 45.

Orange waste has been loaded with various metal ions to create suitable adsorption sites for arsenic and phosphorus. Batch adsorption studies revealed that arsenate and arsenate removal was favorable at pH 5-9 and 9-11, respectively, while phosphate removal occurred at pH 7-10. The maximum adsorption capacity of the prepared gel was evaluated as 42 mg/g for both As (V) and As (III) while 13.9 mg/g for phosphate. Column adsorption studies confirmed that the gel has the potential to adsorb and elute arsenate and phosphate in continuous mode. The excellent anion separation capability of this gel could lead to the development of cost-effective technology for arsenic and phosphorus removal.

The leaching kinetics of cadmium from scallop waste in dilute sulfuric acid was investigated by examining the effect of temperature (293–333 K), pH (1.5–2.5), and particle size on the leaching rate. The kinetics of the cadmium extraction process with intraparticle diffusion was reasonably interpreted according to the shrinking core model as a rate-determining step in accordance with the value of the activation energy, 15.9 kJ/mol. Increasing temperature, and decreasing pH and particle size positively influence the extraction of cadmium from the uro.