Hari Paudyal

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.

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.

Selective recovery of gold using some cross-linked polysaccharide gels

Effective recovery of gold from aqueous acidic chloride media was achieved with different kinds of polysaccharides with different structures by treating with concentrated sulfuric acid. The gels were found to be highly selective for Au(III) over other precious and base metals at varying hydrochloric acid solution. The adsorption isotherms of Au(III) followed the Langmuir type of adsorption and the maximum adsorption capacities for Au(III) was evaluated as high as 7.57, 7.20, 5.64 and 4.80 mmol g−1 for the gels of cellulose, dextran, alginic acid and pectic acid, respectively. Analysis of kinetic data shows that the uptake of gold(III) on celulose gel at the initial stage follows pseudo-first-order kinetics. Crystalline structure of the cellulose before and after the treatment with concentrated sulfuric acid was measured by XRD analysis. Furthermore, Au(III) was found to be reduced to elemental form by all types of polysaccharides gels, which was confirmed by the formation of clearly visible elemental gold particles and by means of the XRD-spectra of the adsorbents after adsorption. Infrared spectrum studies provided supporting evidence for the reduction of Au(III) to Au(0) with a suitable mechanism of Au(III) adsorption followed by reduction using various polysaccharide gels.

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.

Adsorption Behavior of Fluoride Ions on Zirconium(IV)-Loaded Orange Waste Gel from Aqueous Solution

Adsorption of fluoride was studied batch wise from aqueous solution by using zirconium(IV)-loaded orange waste gel to achieve practical utility and evaluate the viability of the adsorption gel. Fluoride adsorption was found to be dependent on solution pH and the maximum adsorption of fluoride was observed at pH 2–4. The maximum sorption capacity of the gel for fluoride was evaluated as 1.2 mmol/g, which was compared to that of zirconium(IV)-loaded Amberlite 200CT, a strongly acidic cation exchange resin, which was only 0.5 mmol/g in applied experimental condition. The influence of high concentration of co-existing anions on adsorption of fluoride was studied to evaluate selectivity and competitiveness of fluoride adsorption. The presence of foreign anions such as Cl−, , , and had no significant effect on fluoride adsorption of the present gel. Adsorption of fluoride from actual waste plating solution was also carried out, suggesting very effective adsorption at a solid/liquid ratio greater than 4 g/dm3. Repeated use of the gel was also successfully examined over ten cycles of adsorption-elution-regeneration without any degradation of the gel. These results suggest that the modified orange waste gel is a promising candidate for fluoride adsorption from aqueous solution.

Adsorptive Removal of Strontium from Water by using Chemically Modified Orange Juice Residue

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.

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 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 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 concentration and temperature on the adsorption of . The optimum removal was observed in the equilibrium pH region 2–3. The presence of co-existing anions showed no adverse effect on removal except . 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 Δ G°, Δ H° and Δ S° indicated that the nature of adsorption is spontaneous and endothermic. The results obtained from this study demonstrate the potential usability of orange waste after juicing as a good selective adsorbent.