Currently, ferrocyanide is the industry standard additive that prevents salt from caking during transport and storage. Unfortunately, it cannot be removed from the brine during primary purification as the ferrocyanide complex is too stable. Unless a special destruction unit is added to the process it ends up in the electrolysis cell where it reacts with chlorine to form Fe(III) and cyanide. Further oxidation steps of the latter may eventually lead to the formation of explosive nitrogen tri-chloride. Whereas, the iron deposits on the electrodes or on/in the membranes, leading to damaged membranes, lower product qualities and increased energy consumption.
Iron(III) meso-tartrate (mTA) was introduced in 2004 by AkzoNobel as an alternative anti-caking agent. This complex is thermodynamically less stable allowing iron to precipitate as ironhydroxide during primary brine purification. The residual tartrate is transferred to the electrolysis cells and fully oxidized to hydrochloric acid and carbon dioxide. No unwanted substances are formed.
Over 10 years of industrial experience with mTA salt have clearly proven the benefits of mTA over standard ferrocyanide as anti-caking agent. Cost savings caused by a reduction of power consumption can be around 5 % in the case of plants with brine acidification. Further savings result from the longer lifetimes of electrodes and membranes and the reduced downtime due to maintenance, as well as increased product purity (less chlorate or oxygen formation).
We are happy to discuss the many benefits of high purity vacuum salt for your particular operations and help you select the optimal anti-caking agent.