In-situ Stabilization Of Pb-Zn Contaminated Soil Using Modified Red Mud Granules

Red mud is the waste from aluminium industries. Based on its potential hydration, a modified red mud granule and red mud-phosphate compound particle were made through rotary drum granulation under normal temperature with adding admixtures and surfactants. These granules were applied in the remediation of Pb-Zn polluted soil. It is an innovative approach to utilization of red mud for remediation.Remediation of artificial polluted soil and mine soil, experiments of leaving and expansion of phosphoric in soil column were conducted. The compositions and microstructures of particles, chemical-physical prosperities of soils, content and changes of phases of metals, leaving and expansion of phosphoric were determined and characterized by XRD, SEM-EDS,ABS.Main conclusions in this study are obtained as follows:1. Modification of the gelling property of red mudThe gelling property of raw red mud (RM) is poor as the initial set time was15.75h and the final set time exceeded48h under water/powder ratio of0.5. So, modification was processed by adding cements, milling and calcination, adjust water/powder ratio. The conditions and compositions of the final set time within2h were red mud powder below0.150mm,5%cement,5-10%gypsum, water/powder ratio of0.5.2. Preparation and modification of red mud granulesProperties of red mud granules manufactured by different granular under different conditions were compared. Rotary drum granulation was distinct from moisture measuring, mixing and molding. Because of the water was easy to dismiss from the small and separate granules, it was a weak gelling through rotary drum granulation. The optimum technological condition of red mud based granule PL was determined as RM (<0.150mm),5%cement,5%gypsum,1%rice straw (<0.150mm), surfactant OP of0.1%through rotary drum granulator.3. Remediation of Pb-Zn polluted soil using red mud granulePL was applied in the rremediation of artificial polluted soil and mine soil to determine the optimum amount and application mode. The effect of using red mud granules were studied in the in situ remediation with leeks and rice used in the pot experiments. And the influence on soil and growth of plants were analysis.Both of RM and PL could decrease the ion exchangeable Pb (Pb-Ⅰ). Comparing to increase of Pb-I after15d, continue notable stabilization was occurred. On soil pH, the increase by using PL was less influential. Compare to RM, the decrease rate was9.76%(adding1%) and13.63%(adding5%).When the soil moisture was maintained20%-25%, the largest decrease rate of Pb-I and Pb-Ⅱ was94.50%and45.95%with5%PL adding into the artificial polluted soil, while the increase of residual Pb was48.46%. The decrease of ionic Pb and Zn was44.79%and100%in the remediation of mine soil. And the increase of residual Pb and Zn was72.26%and45.54%.The advantage of this modified red mud granule was that alkali could be coated in the structure of hydration crystal to dilate the release of OH". So it not only persist the absorption prosperity of re mud but also purse the transformation of phases.4. Preparation of red mud-phosphate composite granule and its applicationOn the base of the application of PL, red mud-phosphate composite granule (signed as PK and PCA) was manufactured by adding soluble and dissoluble phosphate. A further relief of the increase of soil pH was obtained by using these granules to substitute red mud powder.When adding5%composite granule PK4(containing6.80%phosphoric), the transformation of phases was significant that the largest increase rate of residual Pb was81.26%and the decrease of carbonate, iron-manganese oxide and organic phase were78.74%,85.62%,73.46%. With1.70%phosphoric in PK2, the absorption of lead was effectively restrained by68.05%in the case of plants vegetated well.In the leaching experiment, the content of soluble-phosphoric after passing through soil column was the largest as25.89mg/L by adding soluble phosphate in the initial stage. But during5-20d, the release of water soluble phosphoric was in a higher level with adding PK4than adding soluble phosphate, ranging23.34%. Experiment results showed that red mud-phosphate composite granule can stabilize the metals and at the same time relieve the release of phosphoric. This study has tentatively probed in the usage of red mud in remediation of soil and agricultural production. It may provide an idea for future utilization of red mud.