<p>A process for the production of lignin in which lignin is precipitated from aqueous solution by acidification and agitation and the precipitated lignin is separated from accompanying liquid in which the lignin-containing solution and the acid are introduced by simultanteous cocurrent flow into an agitated mixing region, the precipitated lignin is separated not more than 60 minutes after precipitation and the separated lignin is subsequently washed. The process can form a step in a general process for the treatment of lignocellulosic materials to produce one or more products including lignin. The process enables the ash content of lignin to be reduced.</p>
