Study On A New Method For Evaluating The Efficiency Of Scale Inhibitors

The formation of calcium carbonate in the cooling-water system is a common problem and concern of safety.Presently,the addition of scale inhibitors,which is a convenient,economical and high performance measure,is the main method of controlling scale in cooling water system.Therefore,a method which will evaluate scale inhibitors rapidly and exactly is necessary and crucial for water treatment workers.The starting point of this paper is to develop a method to evaluate scale inhibitors which is accurate,reproducible,rapid and easy to use with simple apparatus.A new evaluation method of scale inhibitors-rapid controlled precipitation method or RCP-has been developed and validated in LIM of ENSAM.This method is based on pH measurement.Agitating results in escape of CO₂ in a certain water sample,the concentration of OH^- increases consequently,and OH^- reacts with HCO₃^-leading to CO₃^2-.When the solubility product of CaCO₃ is reached,the precipitation of CaCO₃ occurs.At the same time,the pH value drops due to the decrease in OH^-concentration,and so the point of the precipitation can be easily located.The pH vs. time curve is then drawn.And by referring to the variation tendency of pH value,we are able to determine the scaling potential of cooling-water and the performance of scale inhibitors.pH Curve Method or pHCM has been established based on RCP according to experimental conditions in China.Optimal working condition of the method has been established by laboratory simulation.We considered the saturated CaCO₃ solution with CO₂ as standard solution,three-mouth flask as standard container,800r/min as standard rotational speed,300mL as standard volume,room tempetature as standard temperature(21-24℃).Five scale inhibitors-PASP,PESA,HEDP,Cu²⁺and Zn2²⁺- were evaluated by this method.The experimental results showed that PASP,PESA,HEDP as well as Cu²⁺and Zn²⁺in trace amount are highly effective.Therefore,Cu²⁺and Zn²⁺could be used as new scale inhibitors in the future. The pHCM has the merits of speed,accuracy,simple experimental devices, convenient operation etc.Compared to the static and aeration methods,which are generally used to assess the performance of scale inhibitor,the pHCM has good repeatability and high reliability.The new method matches the long-term proposal on environmental protection and has a bright prospect in applications.