Rust Removal by Electrolysis - A Detailed Illustrated Tutorial, page 41
10. Safety Precautions: Crud & Precipitated Rust Disposal, Prevent Overheating
8) Crud & Precipitated Rust Disposal
In commercial rust removal by electrolysis, waste disposal has to comply with environmental laws and regulations.
If you conduct your home electrolytic derusting, any waste produced during the process - mostly crud and precipitated rust, is exempt from hazardous waste disposal requirements.
But, of course, common sense applies when there is a risk of damaging the local environment.
When you conduct home electrolysis on a large scale, the only two cases of the harmful waste disposal might be the following:
1) Electrolytic solution, crud and precipitate are contaminated with compounds of toxic Hexavalent Chromium which is dissolved into electrolyte from the stainless steel anodes and then partially released in gaseous form as vapor.
2) Electrolytic solution, crud and precipitate are contaminated with trapped Chlorine which first evolves bubbling off the anode, then dissolves in the electrolyte, and, as the electrolyte gets saturated with the chlorine, bubbles out of the solution and rises up along with the oxygen in the mist directly above the bath during electrolysis. Table salt, after it dissolves into its component ions in the electrolytic soltution, is the only source of Chlorine.
The rest of the gross chemical "soup" in a container is relatively harmless, generally consisting of hydrated iron oxides, carbon dioxide, sodium carbonate, calcium carbonate (when sodium carbonate reacts with the calcium ions present in tap water), dissolved components of baking soda (or washing soda), and trapped oxygen and hydrogen gasses. There will also be some minor contaminants depending on how well the iron objects to be derususted have been cleaned of oils, paint, crusted gunk and tar resedue prior to the electrolysis. To sum it up, the chemical soup consists of nothing else besides what one puts in it.
Surfacial Crud (on the left) & Mix of Contaminants and Precipitated Rust (on the right)
The iron-rich dirty electrolytic solution along with crud and gunk can be carefully poured down the drain, as this mix is similar to what already goes into the municipal waste sewers through cast iron pipes. Any amount of the precipitated rust mixed with other minor contaminants can be collected into a plastic bag and then dumped into the garbage can. Of course, you can dump it down the drain if you want to see WHAT might happen to the pipes in your house! (not recommended)
If you have utilized a lot of stainless steel material during electrolysis, and your electrolytic solution has become heavily contaminated with hexavalent chromium, you will have to collect all the precipitates, take them outside, and spread them on a tarpolin under the sun. After the toxic precipitates get dehydrated, place them in a sealed plastic bag, and take it to a designated place at the minicipal landfill. If you have any questions, contact your state's environmental office.
9) Prevent Overheating of Power Supply
Although, most of the modern car battery chargers have cooling fans that prevent overheating, it is important to keep voltage and current below dangerous level to avoid any risk of overheating your power source and other components of the electrolytic setup. Also do not cover the car battery charger with a box or bucket. If tightly covered, the charger will overheat with a possibility of burning up as the cooling fan will be circulating hot air only.
If you are unsure of any of the safety aspects described above or unsure about your safety - STOP! Get help before you do something unwise. Use common sense, be smart about what you are doing, and stay safe so you can finish your iron artifact restoration project and enjoy it.
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