Conclusions

This report presents the state-of-the-art of several technologies for treating and recovering metals from metal-bearing wastewaters and sludges. Only a few of the technologies addressed in this report (e.g., electrowin-ning, high-temperature metals recovery) are directly applicable to the recovery of metals from wastes; other technologies treat the wastes to a physical form that may be amenable to eventual metals recovery. Table 52 presents an overall summary of the potential applicability of the various metals recovery technologies for the Industries and wastes addressed in this report.

Wastewaters can be treated effectively by several methods. Precipitation processes have been widely used to remove arsenic, cadmium, chromium (+3), copper, iron, manganese, nickel, lead, and tine from metal-bearing wastewaters. For economic reasons, electrowinning is a commercial technology that has normally been restricted to the treatment of wastewaters containing noble metals such as gold and silver. For economic reasons, electrodialysis and evaporation are primarily applied to the recovery of electroplating wastewaters. Economic feasibility will depend on the metal concentrations and the values of the recovered metals. Membrane separation is typically used as a posttreatment method for precipitated metal solutions. Carbon adsorption systems have not been commercially applied to any significant extent for metals removal from wastewaters. Ion exchange systems have effectively removed barium, cadmium, chromium (VI), copper, lead, mercury, nickel, silver, and zinc; however, the ion exchange nedia is usually highly selective and not adequate for treating wastewaters containing several metal components.

After appropriate pretreatment, sludges can be effectively treated by high-temperature metals recovery (HTMR) processes. These processes allow for the direct recovery of metals from sludges. The economic feasibility depends on the amount of sludges treated and the amount of metals contained in the sludges. Leaching may be used to extract cadĀ«ium, chromium, copper, lead, nickel, and zinc directly from sludges by using various process trains; however, few leaching process trains have advanced past laboratory-scale tests.

Comnercial waste recycling facilities such as those operated by Recontek in Newman, Illinois, and Eticam in Fernley. Nevada, and Warwick, Rhode Island, employ hydrometallurgical processes for recovery of metals from various categories of hazardous wastes (e.g., F006, F007, D008). Technologies utilized at these facilities include chemical precipitation, leaching, electrowinning, and evaporation.

TABU 5?, SUMMARY TUTRIX SHOWING POTENTIAL APPLICABILITY Of NETALS RECOVERY TECHNOLOGIES FOR HAZARDOUS HASTES IN DIFFERENT INDUSTRIES

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