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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: sdnnet3 on March 15, 2011, 04:05:16 PM

Title: how would you remove hard minerals via electrochem from a water source
Post by: sdnnet3 on March 15, 2011, 04:05:16 PM

i have a pool in the 100,000 gallon range with a very serious scaling problem. this is mostly calcium i believe, but may also have trace amounts of magnesium salts as well. i was curious if anyone knew of an electrochem method to remove it from the water source causing it to break down and migrate to the electrodes.

i am trying to get this done without having to bring up the pH of the pool to react it with the mineral deposits first. i know that with plating you generally need a salt form of what you wish to plate with, but it's been a long while since inorganic chemistry that a lot of these things are escaping me without a massive re-reading of texts.

any ideas of where i could start, electrodes to use for the terminals, and if i would need to increase the pH with hydrochloric acid or not? many thanks for any and all help in advance.

Title: Re: how would you remove hard minerals via electrochem from a water source
Post by: DevaDevil on March 17, 2011, 04:30:54 PM

Quote from: sdnnet3 on March 15, 2011, 04:05:16 PM

... and if i would need to increase the pH with hydrochloric acid or not? ...

adding acid decreases the pH of course...

Title: Re: how would you remove hard minerals via electrochem from a water source
Post by: ajkoer on April 14, 2011, 01:26:37 PM

Solutions include adding a calcium sequestring agent to the pool or complete removal of the water or use ClO2 generator instead of Calcium based chlorinating agents.

 The problem is not necessarily in your source water as you mentioned, but could be from the pool chemicals like Ca(OCl)2 added to the pool. The latter reacts with both the CO2 dissolved in water (to form Carbonic Acid) and the CO2 in the air to form Calcium Carbonate (CaCO3).  The equation is:

                                                     Ca(OCl)2 + H2CO3 --> CaCO3 + 2 HOCl

Also, the Ca(OCl)2 decomposes to eventually add CaCl2 to the pool.

                                                     3 Ca(OCl)2 --> 2 CaCl2 + Ca(ClO3)2
                                                  
                                                        Ca(OCl)2 --> CaCl2 + O2

The addition of this more soluble salts will increase the precipitation of the less soluble CaCO3.  

 The last point is about magnesium contamination. The creation of Mg(OCl)2, even from impurities in the hypochlorite or in the source water, is a serious hazard. Magnesium Hypochlorite is a more powerful and potentially dangerous oxidizer. It has produced a serious self-sustaining fire in a cargo ship that was transporting a hypochlorite solution that apparently contained a Magnesium impurity (Source: Bretherick's Handbook of Reactive Chemical Hazard by P. G. Urben, page 1358, a Google book).

Good Luck.