HEAVY METAL REMOVAL PROCESSES FOR
PLATING RINSE WATERS
R. E. Wing, Research Chemist
W. E. Rayford, Chemical Technician
Northern Regional Research Center
Agricultural Research Service
U. S. Department of Agriculture
Peoria, Illinois 61604
INTRODUCTION
Effective waste treatment processes are needed to meet the stringent effluent standards
that are expected to be set for the electroplating industry in 1977.   This urgent need has
encouraged researchers to develop new chemical and physical processes for meeting these
standards.   It will be costly to design effective treatment processes for the various rinse
waters of the printed circuit industry.   Some rinses will have to be segregated for special
treatments, while others can be processed by conventional treatment.   The use of dragout,
counterflow rinsing, and other water use reduction methods is a good start; however, the
use of plating baths that contain unknown proprietary chemicals does add problems to
treatment design.   The following discussion may suggest solutions to some of the treatment problems.
Over the last few years, numerous publications and patents have appeared describing
technology effective for the treatment of printed circuit plating rinse waters.   Very little
of this technology has gained wide acceptance for various reasons including inadequate
promotion, limited adaptability and unfavorable economics.
For 6 years at NRRC, we have been developing starch-based products for heavy metal
removal.   Starch, a naturally occurring polymer derived from agricultural crops, is very
abundant, annually renewable and relatively inexpensive.   Initially, we used a water-soluble
starch xanthate to bind heavy metal cations in solution and then used a cationic polymer
to yield a polyelectrolyte complex insoluble in water which contained the heavy metals
[1-3].   The use of a two-component system in the process and less-than-favorable economics prevented its broad acceptance.   Therefore, we modified the process to eliminate the
expensive cationic polymer by using a cross-linked, water-insoluble starch as starting material.   We prepared several insoluble starch-based products containing xanthate [4-6],
carboxyl [7], quaternary ammonium [8] and tertiary amine groups [8].   These products
have been evaluated as potential heavy metal scavengers.
INSOLUBLE STARCH XANTHATE
Water-insoluble starch xanthate [4-6] (ISX) offers industry a low-cost product that removes and recovers heavy metal cations from wastewaters (Figure 1).   The effectiveness of
ISX for removing uncomplexed heavy metals from water can be seen in Tables I and II.
The data show that heavy metals are removed from concentrated solutions and dilute
solutions, in most cases to concentrations below present discharge limits.   From these data,
ISX appears to be effective in removing metal ions at different concentration levels.   If
initial metal concentrations in an industrial effluent exceed  100 mg/1, it probably would
not be economical to use ISX, and removal by chemical precipitation or another process
could be used.   In these cases, the ISX could then be used in a secondary treatment to
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