Modern techniques of castings production, including moulding sands production, require a strict technological regime and high quality
materials. In the case of self-hardening moulding sands with synthetic binders those requirements apply mainly to sand, which adds to
more than 98% of the whole moulding sand mixture. The factors that affect the quality of the moulding sands are both chemical (SiO2
,
Fe2O3 and carbonates content) and physical. Among these factors somewhat less attention is paid to the granulometric composition of the
sands. As a part of this study, the effect of sand quality on bending strength Rgu
and thermal deformation of self-hardening moulding sands
with furfural and alkyd resin was assessed. Moulding sands with furfural resin are known [1] to be the most susceptible to the sand quality.
A negative effect on its properties has, among others, high content of clay binder and so-called subgrains (fraction smaller than 0,1mm),
which can lead to neutralization of acidic hardeners (in the case of moulding sands with furfuryl resin) and also increase the specific
surface, what forces greater amount of binding agents. The research used 5 different quartz sands originating from different sources and
characterized with different grain composition and different clay binder content.
In this paper we studied the intensification of the water clarification process on contact clarifiers with quartz sand fil-tering bed, which was modified with a solution of aluminum sulphate coagulant. The modification of the quartz sand filter-ing bed was carried out by applying to the surface of grains of quartz sand solution of coagulant aluminum sulphate with different doses. Investigation of the electrokinetic potential of the filtering material (quartz sand) was carried out by the percolation potential method.
The influence of electrical properties (size and sign of the charge) of the filtering bed itself and suspended solids in the water on the filtration process was studied. The filter material – quartz sand used in contact clarifiers has a negative electric charge. When the electric charge of the particles decreases, that is, as the ζ-potential decreases, the repulsive forces de-crease and it the adhesion of particles becomes possible. This is the process of coagulation of the colloid. The forces of mu-tual gravity between the colloidal particles begin to predominate over the electric repulsive forces at the ζ-potential of thesystem less than 0.03 V.
Modification of quarts filtering bed with a solution of coagulant aluminum sulphate recommended for the purification of surface water allows: to intensify the process of water clarification, to reduce the consumption of reagents by 25–30%, with the obtaining purified water of the required quality, to reduce the production areas necessary for reagent management of treatment facilities, and to reduce the cost of water treatment by 20–25%.