Study Of Stabilization Treatment Technology On Chromium Residue From A Factory In Chongqing

Chromium slag is an industrial hazardious waste, a complex solid waste with difficulty to deal with, has a great harm on the environment, animals, plants, and humans. Chemical stabilization technology, as a new solid waste treatment and disposal technology, has a good advantage of decreaing the volume of solidified compatibilizer and reducing the amount of reagent addition. As heavy metals stabilization agents, organic pharmaceutical agents have many advantages, which can combine with heavy metal ions to form a stable, water insoluble chelate, effectively preventing the leaching of heavy metals. Due to the high efficiency of stable heavy metals, need less of the chelating agent, fly ash or sewage after treatment usually can reach the standard for landfill, which provide effective means for the harmless disposal of chromium slag, but also will have an important value of research and application. In this study, two leaching methods, Horizontal Vibration Method (HVM) and Toxicity Characteristic Leaching Procedure (TCLP), inorganic pharmacies and organic agents were screened by XRD and SEM treatment of chromium slag and chemical stabilization of chromium slag material phase composition and surface morphology were characterized by leaching toxicity experiments to explore the influence of chromium residue and stabilizing treatment of chromium slag of Cr(Ⅵ) leaching of toxic factors, as well as the effect of various pesticides on the stability of chromium slag. The main conclusions are as follows:(1) Chromium slag material composition was very complex, mainly containing CaCO3, alpha-SiO2, Ca(OH)2, MgO, Mg(OH)2, Cr2O3and FeCr24minerals. The surface of chromium slag particle was smooth and dense, with large particle size, showing the irregular shape, spherical particles and needle-shaped crystals, flakes of clay minerals and many irregular condensates. After stabilizing treatment of four kinds of inorganic pharmacies, three kinds of organic acid (salt) pharmacies, and two kinds of thiol flotations, there is no significant change in the phase composition of chromium slag. In particles’surface of stabilizing treatment of chromium slag, the more significant changes occurs. It shows that adding chromium slag can react with chromium chelater in the pharmacy.(2) The pH value of leaching agent Cr(Ⅵ) is the main factor in the impact of chromium slag. Acidic conditions in the water soluble chromium residue of Cr(Ⅵ) leaching, and some acid-soluble Cr(Ⅵ) was dissolved by the acid leaching; neutral conditions, only water soluble Cr(Ⅵ) leaching. The pH values of the three systems are in the range of4.0to7.0, the leaching solution of Cr(Ⅵ) concentration did not change significantly, the leaching solution of Cr(Ⅵ) concentration does not exceed35.57mg·L-1. When the pH of acetate buffer solution is at1.5, the leaching solution of Cr(Ⅵ) concentration increased to48.48mg-L(3) With the liquid solid ratio increases gradually reduce the concentration of Cr(Ⅵ) leaching, the leaching rate of Cr(Ⅵ) increased. Liquid to solid ratio of10:1, the leaching solution, leaching rate of Cr(Ⅵ) began to stabilize, the leaching rate steady at35.31%～36.63%. Cr(Ⅵ) from chromium slag in the leaching process is a quick process to reach equilibrium. With the increasing of leaching time, the leaching concentration of Cr(VI) in leaching solution increases. Generally speaking, the leaching time of8to10hours can be achieved to leach to the balance.(4) Whether it is in the acid or water extraction conditions, compared with untreated chromium residue, the four kinds of inorganic pesticides on the Cr(Ⅵ) in chromium residue has good stabilization effect, which the stabilization effect of the best is Na2S and the worst is FeSO4, the stabilization effect of CaO and Na2HPO4is equivalent to somewhere in between, and acid leaching conditions the stability of the ratio is higher than the water conditionsratio. Adding Na2S2%of chromium slag stabilization rate began to stabilize, the ratio of stabilization in the range of77.60%-87.36%.(5) Whether it is in the acid extraction conditions or water extraction conditions, compared with untreated chromium residue, the three kinds of organic acid (salt) pharmacy Cr(Ⅵ) of chromium slag have a moregood stabilization effect, which the stability of the effect of the best is NT A, EDTA disodium stabilization is the worst effect of DTPA stabilization effect in between. Adding NTA2%of chromium slag stabilization rate began to stabilize, the ratio of stabilization in the range of88.30%-90.90%.(6) Whether it is in the acid extraction conditions or water extraction conditions, compared with untreated chromium residue, the two kinds of chelating agents on chromium slag in the Cr(VI) has a good stabilizationthe effect of ethyl xanthate on the stabilization effect of Cr(VI) is better than diethyldithiocarbamate. Ethyl xanthate solution is8mL, the ratio of liquid to solid is4:5, the ratio of stabilization in the range of88.91%-91.18%.(7) The floc of heavy metals and inorganic pharmacies in neutral and alkaline conditions (pH>8) is relatively stable, but under acidic conditions (pH value<6), it can be partially dissolved in the amount of hexavalent chromium leaching, and increase rapidly with the decrease of pH value. The similar phenomenon was happened in floes of heavy metal and organic chelating agent. To achieve better stabilization effect, neutral or alkaline conditions should be considered for stabilizing treatment of chromium slag.