73    COMPARISON OF PHOSPHATE COMPLEXING OF HEAVY
METALS THROUGH QUALITATIVE ANALYSIS
Kathryn L. Farrell-Poe, Assistant Professor
Agricultural Systems Technology & Education Department
Utah State University
Logan, Utah 84322-2300
James E. Etzel, Vice President
Heritage Environmental Services
Indianapolis, Indiana 46241
INTRODUCTION
Lester1'2 (1987) states that the ultimate cause for concern about heavy metals in the environment is
their extreme toxicity towards man. Both acute toxicity (single dose or multiple doses over a period of
less than 24 hours) and chronic toxicity are of concern.
Metals exist in wastewater in many forms: soluble, insoluble, inorganic, metal organic, reduced,
oxidized, free, precipitated, adsorbed, and complexed. Hence, the treatment of heavy metal bearing
wastewaters can be complex.
In times past, the motto of industrial treatment was "the solution to pollution is dilution." However, with the current pretreatment regulations, effluent limitations are applicable to the treated
effluent prior to dilution with sanitary wastewater, non-contact cooling water, or other non-process
water.3 Industries must either reduce the generation of pollutants in the manufacturing processes or
remove them from the wastewater stream. In some cases, the material removed may be hazardous
under RCRA and thus require special attention.
Hazardous waste management, based primarily on environmental concerns, uses the following
schemes (listed in order of decreasing environmental protection): waste reduction, waste separation
and concentration, waste exchange, energy/materials recovery (the last option before treatment),
waste incineration/treatment, and secure ultimate disposal.4 The best method to control metal bearing wastewaters is to modify the design and/or operation within a process to eliminate or minimize the
production of hazardous material containing wastewater.
In the event that a process can not be altered, there are two alternatives: zero liquid discharge or
treatment. However, it is not always possible to achieve zero liquid discharge either because of
economics or feasibility. Therefore, treatment becomes necessary and is the most common form of
managing heavy metal bearing wastewaters.
The primary objective of treatment is the removal or conversion of the specific hazardous components to a non-hazardous state. Smith5 classifies the treatment of common heavy metal wastewaters as
either a recovery system or solids removal system. He includes in recovery systems such processes as
evaporation, ion exchange (I/E), reverse osmosis (RO), crystallization, distillation, electrolytic recovery, and electrodialysis (ED). The solids removal systems include hydroxide and sulfide precipitation,
sedimentation, diatomaceous earth filtration, membrane filtration, granular bed filtration, peat
adsorption, insoluble starch xanthate treatment, and flotation. With the conventional methods of
heavy metal treatment, Smith groups oxidation/reduction plus precipitation, electrolytic reduction
for recovery, ion exchange for a polishing treatment or for recovery, and membrane or evaporative
separation. Selection of the treatment process is dependent on the nature of the wastewater and the
quality of the effluent desired if recovery or reuse is not feasible.
Triple superphosphate (TSP) has been used with success in complexing heavy metals and producing
a sludge which is non-toxic based on the Environmental Protection Agency's Extraction Procedure
(EP).6"8 TSP is monobasic calcium phosphate, Ca(H2P04), which has been treated with phosphoric
acid (H3PO4). It is used mainly as a commercial fertilizer. Farrell-Poe and Etzel8 summarized the
findings of three investigations on using TSP in treating ion exchange regeneration wastewaters and
EP-toxic sludges.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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