Research On The Co-Adsorption Of Anions And Cations In Wastewater Containing Heavy Metallic Ions

Due to the excellent physicochemical properties of coatings, the electroless nickel plating technique has been widely applied in industrial manufacture, and plenty of spent wastewater is produced. The spent wastewater contained high quantities of anionic and cationic pollutants (Ni2+and H2PO3-/H2PO2-), and small amount of organic pollutants. If wastewater was discharged beyond standards, which was easily to cause water and soil pollution, and was toxic to animals, plants and human. Hence, it is of utmost importance for the removal of nickel and phosphorus from the spent electroless nickel plating wastewater by using an effective and economic technique.Among the approaches in treating spent electroless nickel plating wastewater, dsorption is one of the most promising techniques due to its advantages of operation simplicity, high efficiency, low cost and potential for regeneration. Therefore, this work committed to the adsorption of metal cations (Cu2+, Zn2+or Ni2+) in wastewater and the co-treatment of nickel and phosphorus in electroless nickel plating wastewater by CHTs.The adsorption studies of metal cations by CHTs implied:it was found that the Langmuir model was more appropriate to describe the adsorption isotherm; the maximum adsorption amount was higher than some other adsorbents, specifically, being 6.583,7.535 and 6.152 mmol/g for Cu2+, Zn2+or Ni2+under the proposed conditions; for kinetic data, the pseudo-second-order kinetic model appeared to be the best-fitting model compared to the pseudo-first-order and Elovich models; thermodynamic analysis revealed that Cu2+, Zn2+or Ni2+sorption on CHTs was spontaneous and endothermic; in the reusability study, the sorption capacity of the adsorbent did not vary remarkably in the initial four sorption/calcination cycles for Cu2+, Zn2+or Ni2+removal.The adsorption process of Ni and P in electroless nickel plating wastewater on CHTs showed:adsorption kinetics data of nickel and phosphorus could be well depicted by pseudo-second-order model; adsorption isotherms studies showed that the uptake of nickel and phosphorus on CHTs followed Langmuir and Freundlich models, respectively, and maximum removal of nickel or phosphorus was up to 22.87 or 761.5 mg/g; thermodynamic analysis implied the adsorption process of nickel or phosphorus on CHTs was spontaneous and endothermic. Further, the possible mechanisms were explored:for low concentration solutions, CHTs occurred to reconstitution involving the isomorphous substituting sites of magnesium by nickel in sheets and concomitant utilization of phosphorus by the generated superficial sheets; for high concentration solutions, CHTs rebuilding hydrotalcites structures were influenced and formed mixed metal salts of phosphites, hydroxides, hypophosphites, which attributed to the presence of plentiful phosphorus and brought about the reduced uptake of nickel.As a consequence, CHTs possessed vast application potential in treatment effluents containing Cu2+, Zn2+or Ni2+and treatment spent electroless nickel plating wastewater with high efficiency, easy operation and low cost.