The hot-dip galvanising process uses hydrochloric acid (pickling acid) to clean steel before it is immersed in molten zinc. The waste liquids and fumes generated by the galvanising process have earned the galvanising industry a reputation as environmentally unfriendly. Disposal of the waste fluid generated by the overflow rinse tank - consisting of iron chloride, zinc chloride and unused hydrochloric acid - is the major environmental challenge facing the galvanising industry worldwide.
Cleaner production initiatives
Industrial Galvanisers Corporation Pty Ltd began research into ways of reducing waste fluids from the galvanising process in 1991. Industrial Galvanisers' research and development team saw this as a means of reducing both company costs and improving environmental performance.
Their work led to the continuous electrical preflux treatment (CEPT), which controls the iron levels in zinc ammonium chloride preflux solutions. The process is based on an electrolytic reactor, in which iron in the preflux solution is oxidised to an iron hydroxide precipitate. The dissolved iron had previously rendered the solution ineffective, but its removal as a precipitate means that the solution can continue to be used. This, in turn, reduces the waste disposal requirement by up to 50%.
Advantages of the process
The benefits are:
- a reduction or elimination of waste effluent solutions;
- a reduction in fume levels through optimum preflux controls;
- minimal non-toxic residue.
Following implementation of the CEPT system, one plant has reduced by 50% the amount of contaminated fluids requiring disposal. This, in turn, reduced the load on the environment and cut the plant's annual waste fluid disposal cost of A$200,000 in half.
The introduction of CEPT technology also allowed more detailed monitoring of the condition of the preflux bath, and of the performance of the metal preparation line. CEPT has become a useful management tool, allowing product quality to be improved, and delivering additional savings from improvements in overall plant management.
Cleaner production incentives
The financial benefits of reducing a key production cost, and a desire to help change the image of galvanising as an environmentally unfriendly industry, were the key imperatives for Industrial Galvanisers. The philosophy of cleaner production enabled the two objectives to be combined.