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1 Reference 37. Availability-

PrPSESS maturity—Reverse osmosis has been widely accepted in the electroplating industry for the recovery of metals in rinse water. The technology is available from a fairly large number of membrane and system equipment manufacturers, many of which are listed in the literature.

Locations of operating units—Table 34 presents a list of current RO installations in the electroplating industry.

Environmental Evaluation—

The R0 technology, as applied in the electroplating industry, is a recovery technology capable of achieving zero discharge. Wastes requiring disposal will be minimized, provided the effluent stream can be recycled.

Capital costs of RO units are a function of membrane type and surface area. The packaged RO units contain several identical membrane modules along with auxiliaries such as a feed pump, tank, and pretreatment equipment. Installation costs are low because the units are skid-mounted and require only utility connections. The capital cost of a system is approximately the same for spiral-wound or hollow-fiber membranes. Figure 12 shows the costs for a spiral-wound, cellulose acetate membrane system.

Costs-

TABLE 34. CURRENT RO INSTALLATIONS IN THE ELECTROPLATING INDUSTRY*

Type of bath

Type of membrane and configuration

No. of installations/ zero discharge

Bright nickel Nickel sulfaraate watts nickel

Cellulose acetate Spiral-wound

150/yes

Cellulose triacetate Thin-film composite Hollow-fiber-Spiral -wound

12/no

Zinc sulfate

Thin-film composite Spiral-wound

1/9ÖS recovery of metals

Cellulose triacetate Hollow-fiber

5/90% recovery of metals

Copper cyanide

Polyamide Hollow-fiber

2/90% recovery of metals

* Reference 37.

* Reference 37.

The operating cost for an RO system is lower than that for evaporation because the cost of separating the unit mass of water by RO is much lower than that for evaporation. Additional costs are incurred for membrane replacement and feed pretreatment, however. Also, additional evaporators may be required to produce an RO affluent stream that is concentrated enough for direct reuse as an electroplating solution.

When reverse osmosis alone can be used to produce a satisfactory plating solution, chemical recovery benefits can be appreciable. Table 35 presents a detailed analysis of the economics of a reverse osmosis installation for drag-out nickel recovery from a Watts nickel line.

Donnan Dialysis and Coupled Transport

Two developing membrane technologies are Donnan dialysis and coupled transport. Although neither is commercially available at this time, both show potential for cost-effective recovery of metals from plating solutions.

Both processes use a concentration gradient to drive ions from a spent solution across a membrane and into a stripping solution. These processes use a cell consisting of two compartments separated by a membrane. The waste

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