Peculiar Characteristics
of Chromium
Don E. Bloodgood and Aubrey Strickland
Purdue University
Lafayette, Indiana
At the present time the principal methods for the disposal ol
chromium compounds (1), (2), (3)* are (1) reduction and precipita¬
tion with various compounds with subsequent disposal by burial or
dumping, and (2) precipitation and partial recovery of the desired
constituents by electrolysis. These methods are said to be satisfactory
in some cases. However, they cannot be considered efficient or effective
in producing chromium-free water or in the recovery of valuable
chromium compounds from the dilute waste waters of the metal plat¬
ing industries. Recognition of the need for a better method prompted
studies at Purdue University using commercial ion-exchange resins.
An ion-exchange method would eliminate the necessity for large
settling tanks, large quantities of chemicals, extra personnel, etc., and
in addition would afford a rapid continuous process for detoxifying
wastes and recovering the chromium and perhaps other valuable com¬
pounds.
Early attempts were made to treat metal plating wastes containing
both chromium and cyanide compounds, but it was ultimately con¬
cluded that the complexity of each was such that separate studies of
the two wastes would be more feasible.
At first, tests were made with cation and anion exchangers in series,
using solutions of potassium chromate. It was found that some of the
chromate was removed on the cation exchanger, much more on the
anion exchanger, and some was not removed at all. Sulfuric acid and
hydrochloric acid of various normalities were used for regenerating
the cation exchangers, and sodium hydroxide, ammonium hydroxide,
sodium carbonate, hydrochloric acid, and, because of its molecular size,
tartaric acid solutions were tried for regenerating the anion exchangers.
In no case was the regeneration considered satisfactory, and in all cases
* Italicized   figures   in   parentheses   refer   to   entries   in   the   Bibliography,
page 241.
232