Chloride Salts Removal by non Planted Constructed Wetlands Receiving Synthetic Brines from Belle Plaine Potash Mining

Abstract

Four pilot-scale constructed wetlands (CWs) were employed to study the fate and

transport of the two dominant chloride salts (NaCl and KCl) receiving the synthetic

brine. The characteristics of the brine solution are made up with a 10:1 concentration

ratio between NaCl and KCl based on data obtained from Belle Plaine potash mine site.

The multi-layer soils were designed to function as a main salt filtering component

comprising of Regina Clay (grain size <0.002 mm), Brick Sand (grain size <4.75 mm)

and sharp gravels (grain size between 6.3-19.1 mm) despite the clay layers contained a

poor compact condition (Db =1.4, <1.6 g/cm3). The volume of void space in the

compacted clay was reduced to approximately half the natural state following application

of pressure (4,505 cm3 to 2,743 cm3). The CW systems were operated by the 16-day

format (batch 1-3) and the 4-day format (batch 4). During the 16-day format

experiments, the best K+ removal rate was recorded on Cell2 as 92.1±63.4%

(4.6±5.3mg/l) while Cell 4 contributed the maximum removal of Na+ and Cl- as

44.8±76.7% (53.2±92.4mg/l) and 50.5±109.6% (85.3±184.3.4mg/l). In the 4-day format

operation, the chloride breakthrough curve was discovered in all treatment CW cells,

excluding the control. Moreover, the curve stated at less than 6 hours (C/C0 > 0.05) and

approximately reached the break point (C/C0 > 0.95) after passing 48 hours. Then the

clay media was exhausted and lost its ability to remove Cl-. However, the study was not

able to determine the breakthrough curves in neither Na+ nor K+ cases during batch

experiment 4 due to unidentified ending points on both cations.