Application of Flocculants for the Treatment of Acidic Wastewater
Abstract Generated abstract
This paper examines the treatment of acidic industrial wastewater containing iron, copper, chromium, and other heavy metal ions, focusing on acceleration of metal hydroxide settling after reduction of hexavalent chromium and lime neutralization. Laboratory settling tests were conducted in 500 ml cylinders at 18°C using the flocculants PAA and K-4 at several dosages, with clarification measured over time relative to long-term settled hydroxide volume. The results show that both flocculants increased clarification compared with untreated suspension, but PAA was markedly more effective, especially during the first minutes of settling. The study concludes that PAA can substantially intensify precipitation of metal hydroxides formed during neutralization of acidic wastewater.
Full Text
APPLICATION OF FLOCCULANTS FOR THE TREATMENT OF ACIDIC WASTEWATER
S. A. BABENKO, R. I. TASOEV, O. I. POPOVA
(Presented by the scientific seminar of the Department of Processes, Apparatuses, and Cybernetics of Chemical Production)
The wastewater of one of the Tomsk plants consists of etching solutions having the composition Fe$^{3+}$—70 g/l, Fe$^{2+}$—96 g/l, Cu$^{2+}$—60 g/l, chromium-containing water containing Cr$^{6+}$—1 g/l, and rinse water with a variable amount of heavy-metal ions—0.1–300 mg/l.
As a result of studies carried out on the treatment of wastewater of the specified composition by various methods, a technological scheme was recommended that provides for the reduction of hexavalent chromium by ferrous chloride, which is part of the etching solution, with subsequent neutralization of all the wastewater by lime milk. The metal hydroxide formed in this process precipitates. In order to intensify the process of their precipitation, the flocculants PAA and K-4 were used.
Table 1
Dependence of the clarification of a suspension of metal hydroxides on flocculant consumption
| Flocculant consumption, g/m$^3$ | Clarification percentage, min | Clarification percentage, min | Clarification percentage, min | Clarification percentage, min | Clarification percentage, min | Clarification percentage, min |
|---|---|---|---|---|---|---|
| 1 | 3 | 5 | 10 | 20 | 30 | |
| — | 2 | 12 | 31 | 59 | 77 | 81 |
| PAA—1 g/m$^3$ | 7 | 46 | 68 | 80 | 89 | 90 |
| PAA—5 g/m$^3$ | 19 | 70 | 76 | 83 | 85 | 90 |
| PAA—50 g/m$^3$ | 75 | 85 | 87 | 90 | 92 | 94 |
| K-4—1 g/m$^3$ | 2 | 22 | 45 | 70 | 80 | 82 |
| K-4—5 g/m$^3$ | 4 | 32 | 60 | 75 | 83 | 85 |
| K-4—50 g/m$^3$ | 5 | 32 | 54 | 73 | 82 | 84 |
The experimental procedure was as follows: water samples containing metal hydroxides were poured into a cylinder with a capacity of 500 ml; after adding the calculated amount of coagulant, the percentage of clarification was recorded at definite time intervals. Clarification was taken as 100% when the hydroxides had settled and occupied a volume of 90 cm$^3$ (the hydroxides occupy this volume after standing for one month). The water temperature was 18°C.
As can be seen from Table 1, the addition of the flocculants K-4 and PAA to the suspension accelerates the precipitation of metal hydroxides, with PAA acting more effectively. Thus, at a PAA consumption of \(1 \, \mathrm{g/m^3}\), after 3 min the clarification percentage increases by more than a factor of two in comparison with the suspension without a flocculant (clarification of 68 and 31%, respectively). A further increase in PAA consumption to 5 and \(50 \, \mathrm{g/m^3}\) increases the rate of hydroxide precipitation especially at the beginning of the process. The flocculant K-4 accelerates the process of hydroxide precipitation only slightly even at a consumption of \(50 \, \mathrm{g/m^3}\).
Thus, the use of PAA makes it possible to substantially accelerate the process of precipitation of metal hydroxides obtained as a result of the neutralization of acidic wastewater.