Process for recovering pure lignin derivatives from sludges

摘要

In a process for recovering pure lignin derivatives from sludges, which contain lignin derivatives and heavy metals, by dissolving the lignin derivatives by means of bases and subsequent acidification, the sludge is adjusted to a water content from 70 to 99 % by weight, if required, and a) adjusted with alkalis to a pH of more than 11, the lignin being dissolved and being separated from the solid phase which contains sand, fly ash and the heavy metals predominantly in the form of their sulphides and carbonates; and b) the filtrate from process stage a) is adjusted with acids to a pH of less than 6, the lignin precipitating in a readily filterable form and being separated off, and the liquid phase low in pollutants being disposed of by conventional processing methods.