Darkness had enveloped the Newell Recycling yard by the time Erik Hilario climbed into a front-end loader on a cold evening in January 2011. Just 19 years old, Hilario, an undocumented immigrant, had followed his father from Mexico to an industrial park in East Point, Ga., near Atlanta, where they worked as low-skilled laborers amid jagged piles of scrap metal bound for the smelter.