68    TREATMENT OF DICHROMATE WASTEWATER
FROM A STEEL PLANT
Anthony T. AH, Project Manager
Gore & Storrie Ltd
North York, Ontario, Canada
James M. Toguri, Professor
Department of Metallurgy and Materials Science
University of Toronto, Toronto, Ontario Canada
INTRODUCTION
The types of wastes generated at a large integrated steel mill and the associated environmental
problems encountered are well known. These include air emission, solid waste disposal and wastewater problems. The present study deals with wastewater problems; more specifically, a wastewater
problem experienced at the electrolytic tin and chromium plating lines, hereafter referred to as #2 and
#3 E-lines, respectively.
A schematic flow diagram of the process is shown in Figure 1. At the E-lines, all chromium bearing
wastewater is collected and sent for treatment to an ion exchange system. The ion exchange treatment
scheme consists of two operating trains and one standby. Each train consists of a cation and anion
exchange column in series arrangement. The wastewater initially enters the primary trains-where
sodium and traces of iron and tin cations are primarily exchanged on the resin bed for hydrogen ions.
The wastewater subsequently passes through the anion exchange columns where chromate anions are
removed concurrently with chloride, fluoride and sulfate ions.
Chromium, as well as other ions are removed from the wastewater from the anion exchange
column. The deionized water is recirculated back to the E-lines for reuse. When the anion exchange
column is spent, it is regenerated using sodium hydroxide.
One of the major reasons for using an ion exchange system for treating this wastewater is that the
chromium value can be recovered. Ideally, the recycling of recovered chromium to the plating process
is desired. However, the ion exchange regenerated solution contains sulfate, chloride and fluoride,
hereinafter referred to as contaminant ions. When sulfate ions are present at a concentration greater
than 250 mg/L and fluoride and chloride ions are present at a concentration greater than 50 mg/L, an
racycla
to procass
*2 AND #3
E-UNES
m bea'ir>g wtstc*watr.<
ION EXCHANGE
SYSTEM
datontztd
wotar
■a> Sodium Hydroix}*
CHROMIUM WASTE
LIQUOR
dupoaa to landfill
TREATED
CHROMIUM WASTE
USUCR
Figure 1.    A schematic flow diagram of the process.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
631