Kinetic and Equilibrium Studies on the Zinc Adsorption-desorption Characteristics of Some Promising Biochars in Aqueous Solutions

The present research aimed at investigating zinc (Zn) sorption capacity of the biochars derived from apple wood (WB) and rice straw (RB) feedstocks at two 300 and 600°C pyrolysis temperatures (WB300, WB600, RB300 and RB600, respectively) in aqueous solutions. Kinetic and equilibrium sorption experiments were conducted via batch technique. In equilibrium adsorption experiments, the study used the concentration range of 5-200 mg Zn L− 1 and focused on the solution pH effect on Zn adsorption in biochars under the following conditions: unadjusted and adjusted pH (4 and 6) and three ionic strength levels (0.01, 0.03, 0.1 M KNO3). Zinc desorption experiments were conducted under all above mentioned conditions but without pH adjustment at five separate stages. Kinetic data analysis indicated that Zn adsorption in biochars reached the near steady state within 24 hours with the sorption rate order of WB300 < WB600 < RB300 < RB600. The best fitness was superior to both Elovich and exponential rate models. Also, Zn adsorption isotherms in the studied biochars were shown to fit quite well to Langmuir, Freundlich and Dubinin-Radushkevich models. Zn sorption maxima were found to be 4.3, 16.4, 17.9 and 33.3 mg g− 1, on average, for WB300, WB600, RB300, and RB600, respectively. The initial increased pH solution from 4 to 6 caused an increase in Zn adsorption in RB600, RB300 and WB600, however the sorption maxima in WB300 was detected at pH 4. The rise in solution ionic strength from 0.01 M to 0.1 M dropped the Zn adsorption capacity in all the studied biochars. Findings suggested that rice straw derived biochars showed a better performance than woody biochars in Zn sorption and retention from aqueous solutions. In addition, this ability increased with increasing pyrolysis temperature in both types of biochars. Finally, the study revealed that rice straw biochars, produced at high pyrolysis temperatures, can serve as economical and efficient absorbents for Zn removal from aqueous solutions.

Zinc Adsorption in Different Calcareous Soils

Zinc adsorption was studied for ten selective representative soils according the difference amount of clay content, calcium carbonate and organic matter in Duhok governorate, Iraqi-Kurdistan region included (Kanimasi-1&2, Batofa, Zakho, Assih, Semeel, Khanke, Faydi, Zawita and Bamarny locations). Samples were air dried and sieved through a 2-mm sieve to study the physical and chemical characteristics of the soils, forms of zinc and it’s adsorption. Results showed the soluble, DTPA extractable zinc (available), CaCl2 extractable zinc (exchangeable) and total zinc ranged between (0.29 – 0.94), (0.88 – 1.64), (1.71 – 2.05), and (12.25 – 56.15) mg kg-1 respectively. Negative significant correlation found between soluble zinc with pH, also negative significant correlation found between DTPA extractable zinc with exchangeable potassium, bicarbonate and available phosphorus but positive significant correlation found between CaCl2 extractable zinc with pH, total–Zn negatively affected with pH and positively with HCO3 and sand. Results demonstrated that by increasing added zinc concentration to studied soil zinc will be adsorbed zinc adsorbed greatly at temperature 25°C and 48°C. In general total zinc adsorbed at 25C° in six concentrations was less than zinc adsorbed at 48C°. At temperatures 25°C and 48°C the high total amount of zinc adsorbed found in the soil of Zawita and Zakho respectively, but the lower total zinc adsorbed observed in soil of Batofa and Kani masi-2. The quantity of adsorption affected positively by presence of clay, calcium carbonate, active calcium carbonate and cation exchange capacity and negatively affected by the ion concentration of bicarbonate, calcium, potassium, organic matter and sand content.

Characterization of Activated Coconut Shell Charcoal as a Zinc Absorbent for Used Oil Lubricant

Lubricating oil is classified as B3 waste (hazardous and toxic waste). In the lubricating oil consists of zinc waste which is very dangeraous for healt and environment. So that to handle lubricating oil is used the adsorption method using coconut shell as adsorbent. This study aims to determine the efficiency of zinc adsorption on lubricating oil with stirring speed, percent solvent, mesh size, and mass of adsorbent variation; to learn the equibilium equation of adsorpsion of Zn metal ion on the activated carbon of coconut shell charcoal using Freundlich and Langmuir equilibirium; and to calculate adsorbtion kinetic constanta using the pseudo first model or pseudo second order kinetics approach. Coconut shells was heated at a temperature of 300ᴼC for 1 hour for the driving process . Furthermore, charcoal was soaked in 25% HCl for 18 hours. After being neutralized to pH 7, the charcoal was activated for 3 hours at a temperature of 500ᴼC and stored in a closed place. Coconut shell adsorbent and H2SO4 solvent were put into a beaker glass containing 400 ml of lubricating oil and stirred for 2 hours, every 30 minutes intervals were taken 50 ml to destruction for 2 hours with 68% HNO3. The zinc concentration before and after adsorption were measured using AAS. This study uses the Langmuir isotherm and Freundlich Isotherm models. The greatest efficiency of zinc adsorption with solvent percent variation 0.5% is 95.0567% and 99.9375% in adsorbent mass variation of 10 gram.