Recovery of Aluminum Hydroxide From Fabricating
Plant of Aluminum Products
YOJI FUKUYAMA, Research Engineer
YASUNAO MISAKA, Manager
KENJI KATO, Executive Director
Kurita Central Laboratories
Kurita Water Industries Ltd.
Yokohama, Japan
INTRODUCTION
Aluminum is a light-weight metal that has many uses. Recent statistics show a great
increase in primary aluminum production in Japan. Current projections call for the yearly
production of aluminum to increase from 950,000 tons in 1970 to 2,000,000 tons in 1975.
The United States leads all countries in the production of aluminum, 4,400,000 tons in 1970
(D-
During recent years, an increasing percentage of the primary aluminum production
has been used for making building materials and consumer goods such as window sash,
doors, curtain walls, etc. Ten percent of the total aluminum production in Japan was used
for this purpose in 1965; in 1969, the percentage was 23 percent. This increase in the use of
aluminum for building materials appears to be associated with the development of an
effective surface finishing technique which provides protection against corrosion. Through
the surface finishing process, the aluminum or its alloy is coated with an artificial oxide film
2 to 20 /Jm in thickness. The process of surface finishing of aluminum involves an
electrolytic treatment called anodizing; this provides a longer life and smoother surface to
the aluminum. Wastewater from fabricating plant of aluminum products is mostly
produced by the anodizing process.
The major problem associated with treating anodizing wastewater is the production of
a large amount of aluminum hydroxide sludge. Because of its high moisture content,
disposal of the sludge is often difficult and costly.
The authors have developed an effective method for treating the wastewater from the
anodizing process. The treatment method produces an aluminum hydroxide sludge with a
low moisture content, as a result, aluminum hydroxide can be recovered as a valuable
material. The recovery is one of the distinctive features of the developed treatment method.
Several plants employing the developed treatment method are now working successfully in
Japan.
ANODIZING PROCESS FOR ALUMINUM PRODUCTS AND ITS WASTEWATER
The anodizing process provides a protective anodic film to the surface of the
aluminum. Thus, the aluminum is rendered corrosion resistant. The purposes and
performance conditions of several steps in a typical anodizing process are presented in
Table I (2).
Wastewater from the anodizing process can be classified into two groups, the strong
liquor and the rinse water. The strong liquor consists of the strong alkaline wastewater from
the etching process and the strong acidic wastewater from the anodic oxidation tank
(Figure 1). The characteristics of the wastewater are shown in Table II.
The alkaline and acid wastewaters are discharged intermittently, i.e. whenever the
concentration of aluminum ion in the liquors exceeds a tolerable level. Rinse water is
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