In 1799, after spending the winter at the academy of mines in Freiberg, Aall returned to Norway. Following his father's death, he invested his patrimony in the purchase of the immense Nes Iron-works in the Arendal ore region. After purchasing the iron-works, the operation became more efficient, but was placed in a difficult position at the outbreak of the English Wars in 1801. However, the business persevered.