Ferric Chloride Consumption

The ferric chloride consumption per product is calculated with recovery (see Table 8.16 for values). The ferric chloride consumption per day (or per 1000 m product) gives an indication of the quantities of coagulant to be transported to the plant. 

Table 8.17 Ferric chloride consumption and sludge production.

Process Ferric chloride dosage [mgL- ] Ferric chloride consumption per product g m-5] Ferric chloride consumption per day [kg d Ferric chloride concentration in waste [kg m- ]... 

The reactions when ferric chloride or ferric acetylacetonate is present occur in three stages (1) an initial fast reaction decreasing in rate, (2) an arrest during which the oxidation rate may be very low, and (3) a "sigmoid phase in which an autocatalytic reaction is finally overtaken by reactant consumption. With the ferric (bissalen) chloride complex, the reaction was accelerated but Stages 1 and 2 did not appear (curve 340R, Figure 2). 

The cost of ferric chloride on treatment is determined by consumption of FeCl 3. The cost of ferric chloride depends on location of the treatment plant (transport cost), quality of the ferric chloride (solid/liquid/imported/purity) and quantity purchased. Quoted prices (per kg FeCl 3) ranged from about 0,29 US /kg for a 20 ton local delivery of liquid FeCls to US 7.10/kg for imported, high purity and low quantity FeCl3. It should be noted here that experiments in this smdy were performed with analytical grade FeCls. The impurities in FeCls produced from spent pickle liquor from iron and steel production may not be of concern when used for conventional treatment, but for membrane applications this effect should be investigated. For this reason both ends of the range are used for comparison. 

The ferric chloride concentration in the waste stream varies from 20 g to 5 kg, depending on dosage and recovery. A high consumption of ferric chloride should be avoided, not only for cost, but also for environmental reasons. 

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