For many materials the process of turning them back into useful raw materials is straightforward: metals are shredded into pieces, paper is reduced to pulp and glass is crushed into cullet.

• 对许多材料而言，将它们转变为有用的原始材料的过程是非常简单的：金属物被压碎成碎片，纸被融合为纸浆而玻璃制品则被碾成玻璃碎末。