TABLE OF CONTENTS Zinc tonnage is large but the price is low. Used mainly in sacrificial applications as galvanize coatings. Some zinc sheet is used as flashing in the construction industry. Zinc is the most cost effective means of protecting steel against corrosion. About two thirds of the zinc for galvanizing applications is used to produce galvanized sheet steel. Auto industry is a major market for galvanized steel. In a new car, on average, over 50% of the sheet steel is galvanized. Secondary sources from which zinc is recycled include zinc die-cast scrap, clippings, die-cast slabs and zinc dross.
Scrap metal is delivered to the secondary zinc processor as ingots, rejected castings, flashing, and other mixed metal scrap containing zinc. Scrap pre-treatment comprises Sorting, cleaning, crushing and screening, sweating, and leaching.
In the sorting operation., zinc scrap is manually separated according to zinc content and any subsequent processing requirements. Cleaning removes foreign materials to improve product quality and recovery efficiency. Crushing facilitates separation of zinc from the contaminants. Screening and air classification (see Chapter 3) concentrates the zinc metal for further processing.
A sweating furnace (see Chapter 6) slowly heats the scrap containing zinc and other metals to approximately 364 C. At this temperature zinc melts but the remaining metals do not. Molten zinc collects at the bottom of the sweat furnace and is cooled. The remaining scrap metal is cooled and removed. It is processed by other secondary processing methods (described in the following sections).
Zinc is also recovered from...
