A method for precipitating metal waste is characterized in that the waste which contains one or more dissolved metal salts, is mixed with a boron compound, and the pH is adjusted to a value at which precipitation takes place in the presence of precipitation nuclei necessary for the formation of metal borates.

Provided is a hexavalent chromium treatment agent capable of penetrating inside of a leather and capable of reducing not only hexavalent chromium present in the vicinity of the surface of the leather but also hexavalent chromium present inside the leather into trivalent chromium. The hexavalent chromium treatment agent of the present invention comprises a hexavalent chromium-reducing compound capable of reducing hexavalent chromium into trivalent chromium, a nonionic surfactant, and an aqueous solvent. The hexavalent chromium-reducing compound preferably comprises an organic compound (A) that has a specific structure capable of acting to reduce hexavalent chromium into trivalent chromium, that has a hydroxyphenyl group, and that has no aldehyde groups and no carboxyl groups.

Provided is a practically valuable and economically excellent insolubilizing material for a specific toxic substance: that is useful for insolubilizing treatment for a heavy metal or the like conducted by applying the insolubilizing material for a specific toxic substance to soil or on the surface of the soil; that is capable of effectively insolubilizing and immobilizing the heavy metal or the like; that is capable of making treated matter neutral so as to be reusable and environment-friendly; and moreover that is capable of imparting strength to the treated matter as necessary; and with which the heavy metal or the like is not re-eluted even when the treated matter is exposed to an environment under a neutral condition or an acidic condition. An insolubilizing material for a specific toxic substance to be used so that soil does not reach a strongly alkaline region of a pH of 11 or more, wherein the insolubilizing material for a specific toxic substance comprises an amorphous aluminum compound or a derivative thereof as a main component, or an insolubilizing material for a specific toxic substance to be used so that soil containing a heavy metal or the like does not reach a strongly alkaline region of a pH of 11 or more, the insolubilizing material for a specific toxic substance functioning also as a solidifying material, wherein the insolubilizing material for a specific toxic substance comprises gypsum obtained by adding and mixing, to the gypsum, the amorphous aluminum compound and the derivative thereof in a range of 0.5 to 60 mass parts relative to 100 mass parts of the gypsum, and a method for improving soil using the insolubilizing material for a specific toxic substance.

A method of treating mercury-contaminated material to obtain a treated product having reduced mercury leachability includes the steps of (a) admixing the mercury-contaminated material with a reagent system comprising calcium sulfide (CaS) and trisodium phosphate (TNaP), wherein the calcium sulfide and trisodium phosphate are preferably provided at a CaS:TNaP ratio of from 2:1 to 1:2, on a dry weight reagent basis, and the reagent system is preferably provided in an amount equal to 0.4% to 5% by weight of the contaminated material; and (b) adding water as needed to achieve a moisture content of at least 5% by weight of the contaminated material.

A batch process of remediation of soil and sediment contaminated with toxic metals includes the steps of treating contaminated soil and sediment with a solution containing aminopolycarboxylic chelating agent, rinsing the soil/sediment solid phase to remove residues of mobilized toxic metals, treating the used process waters to recycle chelating agent and clean process solutions and placing the remediated soil/sediment on a permeable horizontal reactive barrier to prevent emission of contaminants. In the batch process, toxic metals are removed from process solutions by alkaline adsorption of polysaccharide adsorbents. By applying alkaline adsorption the efficiency of toxic metal removal from process solutions and alkaline and acidic recycling of chelating agent is significantly improved.

A treatment method for a used ion exchange resin, includes: bringing a used ion exchange resin into contact with a reaction solution, the used ion exchange resin having an ion exchange group with at least a radionuclide or a heavy metal element adsorbed thereon, and the reaction solution containing an iron compound, hydrogen peroxide, and ozone; separating at least a part of the reaction solution in contact with the used ion exchange resin from the used ion exchange resin; and decomposing an organic component contained in the reaction solution separated from the used ion exchange resin.

Disclosed is a method for stabilizing metallic mercury in the form of mercury sulfide. The method includes the following steps: a) dispersing metallic mercury in a polysulfide aqueous solution so as to convert the metallic mercury into mercury sulfide; and b) separating the mercury sulfide.

A method of treating, stabilizing, precipitating, or otherwise removing heavy metal ions contained in a contaminated media, which method includes: providing a sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; contacting said contaminated media containing heavy metal ions with the sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance; and allowing the contaminated media containing the heavy metal ions to react with said sodium-iron-sulfide mineral or crystalline phase, either alone or in combination with a pH adjusting substance, such that the contaminated media containing heavy metal ions form single or mixed metal-sulfide precipitates or co-precipitates.

A treatment method for coal fly ash, and in particular sodic fly ash, comprises 1) contacting the coal fly ash with anhydrite, and 2) contacting the coal fly ash in the presence of water with at least one additive. The material obtained from the contacting steps (1) and (2) may be dried. The steps (1) and (2) may be carried simultaneously or sequentially. The additive may comprise at least one component selected from the group consisting of strontium-containing compounds, barium-containing compounds, dolomite, a dolomite derivative such as calcined or hydrated dolomite, water-soluble sources of silicate such as sodium or potassium silicate, iron-containing compounds, and any combinations thereof. A particularly preferred additive comprises sodium silicate. The method may be effective in reducing the sodium content in the fly ash (Na.sub.2O), reducing the alkalinity of the fly ash, and/or stabilizing at least one heavy metal such as selenium and/or arsenic to reduce their leachability.

One method of treating incinerated waste comprises: size separating at least some of the incinerated waste into a first undersize fraction comprising particles smaller than the first separation size and into a first oversize fraction comprising particles larger than the first separation size; size reducing at least some of the first oversize fraction; size separating at least some of the size-reduced first oversize fraction into a second undersize fraction comprising particles smaller than the second separation size and into a second oversize fraction comprising particles larger than the second separation size; combining at least some of the first undersize fraction and at least some of the second undersize fraction into a fine fraction; and extracting metal from at least some of the fine fraction. Another method of treating incinerated waste comprises extracting metal by froth flotation from at least some of the incinerated waste. Systems are also disclosed.