Method and apparatus for measuring scaling capacity of calcium oxalate solutions using an electrochemically controlled pH change in the solution proximate to a piezoelectric microbalance

A method of measuring the effectiveness of calcium oxalate scale inhibitors comprising

• a) measuring the calcium oxalate scale forming propensity of a continuously flowing solution having a pH of from about 2 to about 3 comprising measuring the rate of deposition of calcium oxalate scale from the solution on to a quartz crystal microbalance having a top side comprising a working electrode in contact with the solution and a second, bottom side isolated from the solution, wherein the pH of the solution proximate to the microbalance is controlled electrochemically at from about 3.5 to about 9 and wherein the working electrode is coated with or made of a conductive material on which the evolution of hydrogen gas does not interfere with the deposition of calcium oxalate onto the surface of the working electrode at the electrochemical polarization necessary to achieve a pH of 3.5-9 proximate to the microbalance;
• b) adding a calcium oxalate scale inhibitor to the solution;
• and
• c) re-measuring the rate of deposition of calcium oxalate scale from the solution on to the quartz crystal microbalance.

An apparatus for measuring the calcium oxalate scale forming propensity of a continuously flowing solution having a pH of from about 2 to about 3 comprising a measurement cell with stirring means and mounted in the measurement cell:

• a) a quartz crystal microbalance having a top side comprising a working electrode for exposure to the solution and a bottom side isolated from the solution;
• b) a surface pH-measuring module for exposure to the solution, the pH-measuring electrode assembly comprising a mesh electrode laid over a pH electrode wherein the mesh is made of the same material as the working electrode of the microbalance;
• c) two reference electrodes for exposure to the solution;
• and
• d) two counter electrodes for exposure to the solution,
• wherein the quartz crystal microbalance and the surface pH-measuring module are mounted horizontally oppositely oriented, the two counter electrodes are mounted vertically and located each at an equal distance and downstream from the quartz crystal microbalance and the surface pH measuring module and the reference electrodes are mounted vertically and located each at an equal distance and downstream from the each of the counter electrodes and wherein the working electrodes of the surface pH measuring module and the quartz crystal microbalance are coated with or made of a conductive material on which the evolution of hydrogen gas does not interfere with the deposition of calcium oxalate onto the surface of the working electrode at the electrochemical polarization necessary to achieve a pH of 3.5-9 proximate to the microbalance.

A method of measuring the effectiveness of calcium oxalate scale inhibitors comprising

• a) measuring the calcium oxalate scale forming propensity of a continuously flowing solution having a pH of from about 2 to about 3 comprising measuring the rate of deposition of calcium oxalate scale from the solution on to a quartz crystal microbalance having a top side comprising a working electrode in contact with the solution and a second, bottom side isolated from the solution, wherein the pH of the solution proximate to the microbalance is controlled electrochemically at from about 3.5 to about 9, wherein the working electrode is coated with or made of a conductive material on which the evolution of hydrogen gas does not interfere with the deposition of calcium oxalate onto the surface of the working electrode at the electrochemical polarization necessary to achieve a pH of 3.5-9 proximate to the microbalance and wherein the pH of the solution proximate to the surface of the microbalance is measured using a surface pH measuring module comprising a mesh electrode laid over a pH electrode wherein the mesh is made of the same material as the working electrode;
• b) adding a calcium oxalate scale inhibitor to the solution;
• and
• c) re-measuring the rate of deposition of calcium oxalate scale from the solution on to the quartz crystal microbalance.

An apparatus for measuring the calcium oxalate scale forming propensity of a continuously flowing solution having a pH of from about 2 to about 3 comprising

• i) a quartz crystal microbalance having a top side comprising a working electrode for exposure to the solution and a bottom side isolated from the solution;
• and
• ii) a surface pH measuring module comprising a mesh electrode laid over a pH electrode wherein the mesh is made of the same material as the working electrode,
• wherein the pH of the solution proximate to the microbalance is controlled electrochemically at from about 3.5 to about 9 and wherein the working electrode is coated with or made of a conductive material on which the evolution of hydrogen gas does not interfere with the deposition of calcium oxalate onto the surface of the working electrode at the electrochemical polarization necessary to achieve a pH of 3.5-9 proximate to the microbalance.