Neutralizing Sodium Hypochlorite

Inquiring minds want to know ... Why do you want to put sodium hypochlorite + sodium thiosulphate on your plants and what are the plants?

Don't want to do that for sure, not trying to feed plants, just trying to insure that the chemicals I use on the roofs don't, as a byproduct of a mold and algae free roof clean, kill or stunt the perimeter growth......My goal is to totally neutralize the hot roof mix with the first rinse, one that could bring the effluent to epa levels of onsite disposal, one that won't damage the landscaping as we go......Thank you for your reply......

Sounds like a lot of sodium, since the plants actually do not need it and the added salt can be a problem for the plants. The chlorine doesn't help either, though it doesn't really hurt, except for the salt effects. On the plus side the sulfate is a macro nutrient.

How much liquid do you have? Is this a one-time-only operation?

Thanks for taking the time to respond to my questions.......As a matter of practice, though my hot water pressure system will clean any Florida mold ridden roof without chemicals, we are faced with the very many asphalt tile roofs that need very low pressure and very careful treatment, so, lots of these about, a lot to think about before venturing out as just another "Chlorine Cowboy"......Not that they don't have lots of experience and knowledge in the art of soft pressure washing roofs, with the most responsible making sure plants are covered etc in the process, but for me, a sincere effort should be made to fully neutralize the foam like product that was placed and allowed to dwell until the sodium hypochlorite has fully done its job.......These so called cowboys, sometimes are not treated fairly, because they put much time into getting the best job at the least damage, some, many even, no damage at all, and I respect that, but I would like to think outside the box for a bit to see if there is a way to fully wash the effluent and solvent, given one more neutralizing step, to a ph of 7 if possible, well before it all flows to the gutters and beyond, or just rolls off the roof edges that don't even have gutter protection to the landscaping below......Thanks again for any thoughts you might have to guide me........

so sorry, forgot to answer part of your question......Depending on the roof size, five to maybe ten gallons of 6%, 60,000 ppm would be involved.......With what I think I know, my selected neutralizer would need to be about six times this, or in the 360,000 ppm range.......Daunting to me, just the numbers are......Looking for the gallons required, the conversion from a volume of my work to gallons of dispersal?.....Is this effort at all practical, if so, a big boon to this roof clean business, if not, well, back to the drawing board.....

Are you trying to neutralize the pH or reduce the hypochlorite to chloride. Thiosulfate would be one way to reduce the hypochlorite, but not very effective way to reduce the pH. Of course, hypochorite is unstable in acid and can degas. Ferrous Iron is another way to reduce hypochlorite or other reduced metals. I mention ferrous iron, because it is another plant nutrient. I am not sure what the 360,000 ppm has to do with the volumes, that should be a measure of the estimated concentration in the solution you would need. All this really means is a percursor step to estimating the mass of Thiosulfate needed.

Also, Thiosulfate is typically added way in excess to fully reduce oxidized compounds, this means that the available supply of reducing agent doesn't limit the reaction rate, only the available reactant (i.e. faster reaction kinetics and more complete reaction).

Thanks for you repy and informative comments......My thought is, that if I reduce the ph to 7, then I should have an rinse effluent washing into the gutters and away that, by its neutrality would not harm the plants and vegetation, lawns etc that might be in the runoff area.....However, any reducer or application method that would insure a no landscape damage result would be a success......That the reducer selected actually fed the plants, well, that would be a great bonus.......I do believe that the ppm numbers that were given to me are not at all accurate, they seem way out of line given that our five gallons of cleaner in basically Sodium Hypochlorite at 13% in a 40% solution, the 60% being mainly water......Therefore, by dilution we are applying a 6 1/2% SH with a ppm of 60?.......Should this be the case, then is not our problem the SH ppm reduction to zero (or close) with the sodium thiosulphate or equivalent?......The final question being how much of the ST is required?....

Umm, the hypochlorite itself is a strong oxidizing agent, and could kill the soil ecosystem and harm the tissue of the plant root system. Also it reacts with organic mater in soil to form halomethanes. Though as always volume and concentation are the issue. But, the addition of sodium in a concentrated area could be just as harmful to the plants. also, bear in mind that the reaction is in terms of mmoles, and ppm is in terms of mass concentration per liter of solution. Sodium Thiosulfate has a molar weight of 158.1 g/mole, sodium hypochlorite has a molar weight of 74.4 g/mole. In a balanced reaction 1 mole of sodium thiosulfate will reduce 4 moles of sodium hypochlorite. This would mean you need at least 0.53125 grams of Sodium Thiosulfate per gram of Sodium Hypochlorite. However, depending on how much unreacted residuals of hypochlorite are allowed to remain, the typical process is to add excess thiosulfate, as the reaction kinetics depend on the reaction time allowed, temperatures (pressures, solvents, and contaminants also) and the concentrations. Thiosulfate will also react with such things as ferric iron in the water, so other secondary reactions need to be accounted for as they limit the effectiveness of the reductant on the hypochlorite anion.

Again, thanks for your info on this......And, a special thanks for quantifying the reduction problem with real numbers, been searching for this for more than a few days now.....Given this info, I can test the possibilities in the real world of our particular water supply for one, which I do know contains a good deal of iron, and as you have so ably pointed out, this would have a measurable effect on any reduction attempt......What I can do at this point is to calculate the SH weight in solution, then given varying amount of ST added, test each resulting reduction to see what percentage over the theoretical will do our job the fastest and most complete.......Question is, what am I measuring?.....Ph seems the likely? Additionally, in the real world of this, there are copious amounts of water warmed to about 90 to 100 degrees used in the rinsing, which, hopefully will dilute and degrade the chlorine in this great wash of things faster and further, with the resulting effluent benign enough after all this, that there should be no worries about plant damage......I can see that I have a lot to learn about the chemistry of all this, and I do appreciate your knowledgeably responses.......

the pH would not be a good indicator of the hypochlorite concentration, rather you would want to measure active chlorine, a colorimetric pool test kit would be one method to measure chlorine. Free chlorine residual would represent hypochlorite, total chlorine migth represnet other forms like chloramines, as well as the hypochlorite. Once reduced the colorimetric test should show no free (active) chlorine residual. For very low concetrations you would need photometric testing to precisely determine the concentrations remaining. But for a calibration run of trials I would use a cheap pool kit and then go just beyond the measured minimum needed. These are usually responsive down to a precision of about 500 ppm, but this depends on any coloring agents present in the water as the indicator solution turns yellow. you can plot approximately how much it takes to go each percent of change roughtly, best fit a line. Then figure out how much volume it would take to react with 500 ppm, then titrate back to 500 ppm active and determine the volume necessary to get to 500 ppm, and add the calculated extra volume, plus some for reaction.

Be aware, there are other agents such as organic compounds that can interfere with the reducing agents also.

Thanks much for your info and prompt reply.....I will do as you suggest and see what results....Didn't mention it before, but since you advise caution about other compounds that might be present that could interfere with the reduction, what about these two, sodium acetate and sodium citrate, both in fraction percentages within the same solution, as well as a small amount of non-ionic surfactant?......Also, for my understanding, once the active chlorine has effectively been removed, roughly what might my expected effluent ph be at this point??

Might be a bit late, but I'm thinking with the "copious amounts of water warmed to about 90 to 100 degrees used in the rinsing", you just may find that the degradation and dilution might be enough to take your concerns away. As suggested by RCE, use the swimming pool chlorine tester to confirm concentrations are not high. In my opinion, there is no inherent harm in sending swimming pool water (which is what your effluent might end up being close to) to the garden or drain.

Thank you as well for taking the time to respond to my inquiry......I was hoping that the warm water, a lot of it would have a profound reducing effect and it sounds like it would.....Including a warm water test along with the other tests suggested using our particular high iron content water should yield a local result that we can run with.....These comments and suggestions have been enormously helpful......Thanks again......

I am starting a roof cleaning company in Cleveland, Ohio and was investigating this same topic. I am very interested on what you have learned and/or discovered. Please forward any information you think would help. *

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Neutralizing Sodium Hypochlorite 12.5% - Chemistry - Science Forums