Column Leaching Equipment

This equipment is used to study the movement of water and contaminants, tracers, nutrients, colloids, etc. through soil. The equipment can be used for saturated or unsaturated flow and transport studies.

 

 The major components of the system are:

 

1. Syringe pump by ”Four-channel peristaltic pump:”

 

2. Fraction collector  *SMS does not sell but recommends

 

3. Vacuum chamber (unsaturated flow only)

 

4. Soil column (flow cell)

 

5. Vacuum/pressure regulator.

 

 

The peristaltic pump is used to apply water and chemicals to the top of a soil column at a precisely controlled rate. The flow rate depends on the objectives of the study along with a number of other variables such as the diameter of the column and the saturated hydraulic conductivity of the material in the column (i.e. how fast can the fluid be moved through the soil). The leaching solutions can be applied to the top of the column using one dispensing tube, or all four tubes. Note that by applying leaching solutions at several places on the top of the material inside the column one achieves a more uniform application.

 

The fraction collector is placed inside the vacuum chamber. It stores effluent from the column in small volume increments, which can be analyzed for their chemical constituents. The fraction collector has to be small enough to easily fit inside the vacuum chamber.

 

For unsaturated soil transport studies, the soil column is placed on top of a vacuum chamber in such a way that the bottom outlet of the column enters the vacuum chamber through the top of the vacuum chamber. The pressure inside the vacuum chamber is maintained at less than atmospheric pressure (partial vacuum). This causes a negative pressure at the lower end of the column and causes soil pore water to flow directly into the collection tubes of the fraction collector. With this system, unsaturated conditions can be maintained inside the soil column, provided the water application rate is less than the saturated hydraulic conductivity of the soil in the column. To measure the matric or pressure potential of the unsaturated soil, tensiometers may be placed in the column. SMS has small elbow tensiometers as well as transducer tensiometers, which can be inserted through the column wall and fastened with compression fittings. With these tensiometers, one can determine the matric potential inside the soil and check whether (for example) the matric potential is approximately the same along the length of the column. During column leaching studies, the matric potential should preferably be the same at each position in the column.

 

For saturated column studies it is not necessary to use a vacuum chamber. The leaching solution is pumped through an inlet in the bottom of the column and from there upwards to the top of the column. A short section of tubing, connected to an outlet in the top of the column, conducts the column effluent to a fraction collector.

 

SMS recommends the use of a precision vacuum regulator to maintain partial vacuum in the vacuum chamber.

 

 

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