13.4 Optimal Conditions for Arsenic Separation Set under
Laboratory Conditions for the Target Groundwater
Ferrates exhibit alkali reaction with water. Therefore, the pH rises as the amount of
ferrate increases. pH values, oxidation–reduction potential (ORP), and temperature
were continuously measured during the reaction of groundwater with ferrate. Laboratory tests confirmed the optimal pH value for As removal to be 7.0 (see Fig. 13.1).
Further decrease in the pH value leads to lower ferrate stability.
Maximal oxidation–reduction potential E h measured during the reaction reached
850 mV. This value confirms strong oxidizing environment. Optimal reaction time
was set to 20 min, including adding the ferrate, adjusting the pH, and adding a
polymeric flocculant. It was followed by 10-min ageing enabling possible sedimentation and by another 15 min of three-phase filtration.
13.4.1 Laboratory-Verified Conditions for as Removal from
Groundwater Using Ferrates
• pH: after adding the ferrate, adjust the pH to 7 with HCl
• Redox potential: ORP E h maximum 850 mV; max measured ORP on AgCl
electrode 630 mV
Fig. 13.1 pH optimization for dosing of commercial ferrate to get a maximal As removal in water
KLU (see below)—a laboratory test
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Laboratory Conditions for the Target Groundwater
Ferrates exhibit alkali reaction with water. Therefore, the pH rises as the amount of
ferrate increases. pH values, oxidation–reduction potential (ORP), and temperature
were continuously measured during the reaction of groundwater with ferrate. Laboratory tests confirmed the optimal pH value for As removal to be 7.0 (see Fig. 13.1).
Further decrease in the pH value leads to lower ferrate stability.
Maximal oxidation–reduction potential E h measured during the reaction reached
850 mV. This value confirms strong oxidizing environment. Optimal reaction time
was set to 20 min, including adding the ferrate, adjusting the pH, and adding a
polymeric flocculant. It was followed by 10-min ageing enabling possible sedimentation and by another 15 min of three-phase filtration.
13.4.1 Laboratory-Verified Conditions for as Removal from
Groundwater Using Ferrates
• pH: after adding the ferrate, adjust the pH to 7 with HCl
• Redox potential: ORP E h maximum 850 mV; max measured ORP on AgCl
electrode 630 mV
Fig. 13.1 pH optimization for dosing of commercial ferrate to get a maximal As removal in water
KLU (see below)—a laboratory test
302
M. Heřmánková et al.