An investigation has been carried out on the recovery of lignosulphonate from the spent liquor from a calcium bisulphite wood pulping mill.
The mill uses mainly Eucalyptus wood and the spent liquor contains 16% total dissolved solids rich in lignosulphonate, sugars and acetic acid.
The lignosulphonates and saccharides are both potentially useful components and in any water reclamation scheme, recovery of these constituents could be an important aspect.
This paper is primarily concerned with the use of ultrafiltration for the recovery of lignosulphonate.
Exploratory tests were carried out on a laboratory flat sheet rig.
A range of ultrafiltration membranes with different molecular mass limits was used.
The lignosulphonate liquor however, tends to throw down a dynamic membrane which effectively alters the 'normal' separation characteristics of the membrane chosen.
In all cases, there was a dramatic drop in flux due to the components of the liquor.
This was followed by a slower decline related to concentration. However, tests showed that lignosulphonates can be recovered from spent liquor by ultrafiltration and the ratio of sugars and acetic acid to total solids in the starting feed can be i creased Concentrations of over 300 gl-r significantly in the permeates. total dissolved solids were achieved at reasonable flux rates.
The precipitation of ellagic acid and calcium sulphite during the course of filtration must be allowed for in operating procedures.
Conventional membranes should be available in suitable module forms such as plate and frame or tubular forms.
These modules are more suitable to an effluent which is likely to deposit solids during separation.