Retrieval Of Heavy Metal Ions By Electro-concentrating Technique

Toxicity heavy metals can destruct the environment and threat human health directly or indirectly through the food chain; and moreover, discharged wastewater in some industries, such as the electroplating industry or electronic industry, contains heavy metals and even precious metals, which is worthwhile to be recovered. While traditional methods target on the purification of wastewater, and pay less attention on the recovery of heavy metals in the wastewater.Electro-deionization technique, as a new developed technology, performed well in purification of wastewater containing low concentration metal ions; though the metal ions were recovered from the wastewater along the purification process, no research ever studied the enrichment of low concentration metal ions to high concentrated solution to reuse as the industrial raw materials. In this paper, three relevant experiments were conducted to enrich the metal ions for a low to a high concentration:key factors influencing the enrichment were analyzed first, then the multistage enrichment experiment was conducted to get the high concentrated solution, and based on the firt two experiments, rinsing water containing nickel ions was used to verify the technical feasibility.The first experiment had emphatically analyzed adsorption and regeneration of the resin, and determined the contribution sequence of the factors to the concentration by regression analysis. It was found that keep failure proportion of the resin in a certain range, or the effluent would not meet the discharge standards; about the influencing factors, influent concentration made the largest contribution to the enrichment, followed by flow rate; while the voltage should be improved along with the increase of the flow rate and influent concentration to promote the ion migration.Based on the study above, the experiment of three-stage enrichment of copper ions was conducted. The initial solution was concentrated to2.76x104mg/L from45.00mg/L in24hours, of which the enrichment factor was more than613. In the first stage, concentration of copper ions in the effluent was less than0.40mg/L, and the removal rate was more than99.20%; precipitation did not occur in this experiment. So EDI device could achieve the high concentration of copper ions and also the purification of the wastewater. By calculation,0.23yuan was gained for the treatment of each ton of electroplating wastewater containing50.00mg/L copper ions.In the last experiment, electroplating wastewater containing nickel ions was enriched in two stages. The nickel ions were concentrated to10470.83mg/L from the beginning of173.49mg/L, and the enrichment factor was up to60. Enrichment factor of sulfate ion reached94. Combining the last two experiments, recommendations to minimize the wastewater emissions in electroplating industry were suggested.From all the experiments above, EDI device can achieve the enrichment of metal ions from lower concentration to higher concentration in a short time, and also obtain purified water, which is an energy saving, economical method.