OPS Colloids Stabilised with Organics

500 mL of organics at double concentration was prepared, and the pH adjusted. The particles were added and the mixture stirred at 270 rpm for one hour. Then 500 mL of double concentrated background salt solution of adjusted pH was added and stirred at 270 rpm over night. The pH was adjusted prior to mixing the solutions and pH and conductivity were measured prior to the start of the filtration experiment. 

Two sets of equipment were used for coagulation experiments - a conventional jar testing apparatus with six 500 mL cylindrical beakers with an overhead stirrer each, and a Heidoloph RZ R2021 overhead stirrer. The paddle was identical for both stirrer types (1 cm by 4 cm rectangular plate). The jar tests were used for screening tests and MF experiments. In that case the FeCl r was added from a 20 mM (5.4 gL FcCls 6H2O) stock solution, the soludon was then rapidly mixed at 100 rpm for 2 minutes and then at 25 rpm for 20 minutes. The method was adapted from Dennett et al. (1996). 

With the single overhead stirrer, the solutions were stirred for 2 minutes at 100 rpm, then for 20 minutes at 35 rpm (minimum of stirrer). No pH adjustment was made after the addition of ferric chloride. 

At 100 mgL FeCh in general no visible floes formed. The solution was dark yellow in colour. At 25 mgL floes formed rapidly. The floes partly floated or settled and broke ver) easily. The floe formation could be influenced by solution chemisttyt 

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Figure 4.19 Postulated structures (A) stable hematite colloids in absence of organics, (B) reaction limited aggregation (RLAJ, (C) diffusion limited aggregation (DLAJ, (D) SPO aggregates with organics, (E) OPS colloids stabilised with organics, (F) OPS colloids stabilised with NOM, (G) OPS colloids stabilised with organics and destabilised with calcium.

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