Page 210 - Materials Chemistry, Second Edition

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Sustainability of Municipal Solid Waste Management
as the aluminum content reacts with sulfuric acid forming aluminum sul-
fate. Polyethylene remains suspended in the resulting aqueous solution of
aluminum sulfate. The polyethylene is obtained by filtering the solution
using filter paper.
Aluminum Sulfuric acid : Aluminum sulfate Hydrogen

2Al (s) 3H 2 SO 4(aq) : Al 2 (SO 4 ) 3(aq) 3H 2(g)

Using sodium hydroxide
This process involves the addition of sodium hydroxide (NaOH) dissolved in
water to the residual mixture. Sodium hydroxide solution is added to the
PE/Al mixture. Hydrogen gas is produced as the aluminum content reacts
with sodium hydroxide forming sodium aluminate. Polyethylene remains
suspended in the resulting aqueous solution and the polyethylene is obtained
by filtering the solution using filter paper.

Aluminum Sodium hydroxide : Sodium aluminate Hydrogen

2Al (s) 2NaOH (aq) : 2NaAlO 2(aq) H 2(g)

The aluminum chloride resulting from the addition of hydrochloric acid is
considered one of the most widely used aluminum compounds. It is employed
in the manufacture of paints, antiperspirants, and synthetic rubber. It is also
necessary for converting crude petroleum into gasoline, diesel and heating
oil, and kerosene (BookRags Inc., 2005). The aluminum sulfate resulting
from the addition of sulfuric acid is also known as papermaker’s alum. It is
used in the papermaking industry as it can react with small amounts of soap
on paper pulp fibers producing gelatinous aluminum carboxylates, which
coagulate the pulp fibers into a hard paper surface. It is also used for making
aluminum hydroxide, which is used at water treatment plants to filter out
impurities, as well as to improve the taste of the water (Wikipedia, 2005).
The sodium aluminate resulting from the addition of sodium hydroxide is
used in water softening systems. It is also used as a coagulant aid, to remove
dissolved silica, and is used in the construction industry to accelerate the
solidification of concrete and in the paper industry for producing fire brick
and alumina (Wikipedia, 2005).

5.12 Recycling of Food Waste

Food waste recycling can take place through aerobic fermentation (compost-
ing) or anaerobic fermentation (biogas). Composting is the recommended
method for recycling food wastes. Composting is a process that involves