At present, I encountered a more difficult problem : how to remove heavy metals in high concentration humic acid concentrate, while retaining humic acid. We used a multi-stage membrane equipment to separate and concentrate the landfill leachate, extract the humic acid in it, and intend to use it as a soil fertilizer, but the heavy metals contained in it limit its utilization, so we put forward the topic of reducing the heavy metals in the humic acid concentrate. The specific characteristics of the concentrated solution are as follows : high humic acid content, more than 80 %, total TOC = 24000mg / L ; contains nickel, chromium, zinc, cobalt and other heavy metals, content = 3-15mg / L ; calcium and magnesium content = 5000mg / L.
Before , we initially envisaged the use of alkali-modified activated carbon, when the dosage is large enough ( 200g / L ) can indeed remove heavy metals, but bring a large amount of humic acid loss ( 25 % ) ; in addition, we tried to adjust Ph by adding alkali to form metal salt precipitation, but the removal rate was not high, and the precipitation process was accompanied by co-precipitation of humic acid. Therefore, now we still want to try to use carbon, want to seek everyone 's help, whether through the relevant modification means, reduce the adsorption capacity of humic acid at the same time, improve the binding capacity of heavy metals ? Or simply can reduce the adsorption capacity of humic acid method ?
Hello,
it will be difficult to find a specific adsorbent... I would be curious to know what about using bentonite? If you have time/ possibility to do some literature data research or laboratory tests.
Hi, it seems to be an interesting task. Do calcium and magnesium make a problem? Heavy metals are bound to humic acid by strong complexation and ion exchange. I believe a straightforward use of common extragents including activated carbon does not help if the binding was due to ion exchange. There is nothing in actgivated carbon which make replace metals in humic acid. Activated carbon as almost any other extragent does not help to exchange bound metals. I would think about decreasing pH, not increasing - humic acids remain indeed precipitated, however, perhaps a good wash of the precipitate by acidic solution could remove exchanged cations, yet keeping improved humic acid precipitate. Another option could be perhaps washing of precipitate by a concentrated solution of sodium or calcium ions, in hope they will exchange/replace bound heavy metals. The latter could be made also with dialysis against of some salt solutions. The real question is whether bound heavy metals are capable of, in principle, exchange or replacement. Is iron making a problem for a final product? If not, it could be also used as a potential replacement of heavy metals. And, finally, if to look for something which makes better complexes than humic acid, what is about some washing with EDTA or similar substances commonly used to extract heavy metals from soils? It will possibly contaminate humic acid, but then, the humic acid precipitate may extensively be washed with acids which remove ammonium-containing ligands. of course, such an use of extractors is somehow similar to use of adsorbents;. extraction per se does not remove exchanged cations but may compete as a complex-forming substrate producing water-soluble complexes
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