Study On Leaching Mechanism Of Heavy Metal In Cemented Paste Backfills

When tailings are stored in tailings pond for a long time,it is easily to oxidized and then produced acidic water,cause residual heavy metals to enter groundwater or soil.Cemented filling method is widely used for tailings treatment because of its low cost and high feasibility.In order to understand the leaching behavior of heavy metals in cemented filling bodys,setting the solid-liquid ratio 1:5,the pH value of 2,4,6,temperature of 20?,35?,50?,and experiment time of 90 days.The change of the pH value and heavy metal ion concentration were measured by the pH instrument and the full spectrum direct inductively coupled plasma emission spectrometer.The optimum level of heavy metal leaching was obtained by using the orthogonal test table.On this basis,the distribution of heavy metal form in the cemented filling body was obtained by using the modified BCR method,and the X-ray diffractometer and scanning electron microscope were used to get the microstructure of cemented backfill.At last,the leaching mechanism of heavy metals was obtained.The conclusions are as follows:(1)In the 90-day experiment,the change law of pH value was as follows: three solutions with initial pH is 2 showed a consistent trend,and pH value was stable at 2.The three solutions which initial value pH is 4 was consistent,and the pH value increased rapidly on the second day of experiment,and the solution showed strong alkaline,but with the change of time,the pH value of the three solution which initial setting pH is 6 was stable at 10~12.(2)The leaching solution was extracted at a fixed time point,and the content of heavy metals was measured.The results showed that the leaching amount of heavy metals in Fe was the most,and it was leached under the conditions of pH=2,4 and 6.The leaching of Manganese,Znic,Nickel,Cobalt and Copper showed the trend of continuous leaching;Chromium began to leach at 28 days under pH=2;Mo is leached under the condition of pH=6.(3)The optimal level analysis of heavy metal leaching experiments is carried out by using the modified orthogonal table.The optimum solution for extraction of heavy metals in this experiment is pH= 2,the temperature is 50?,and the experiment time at 90 days.(4)According to the morphological analysis of heavy metals,the water soluble state and weak acid extraction state of Fe appeared at 28 days.28 days before of the experiment,Manganese,Copper and Nickel contained the weak acid extraction state which was easy to transfer.The water soluble state appeared at 28 days,and the proportion of two stages gradually decreased.Znic contained water soluble and weak acid extracted state in all six time,showing a continuous leaching activity.Cobalt had a weak acid extraction state 28 days ago.At 60 days,the main forms contain oxidizable and reducible states,which indicated that Cobalt had changed to a more stable form,and it still had potential leaching toxicity.(5)Through the XRD analysis picture of the cemented filling bodies,it was found that the main peaks were quartz and gypsum.At the 28 day,the gypsum's peak was stronger than quartz's,and the number of diffraction peaks became more.By comparing the SEM diagram of the samples before and after the experiment,it was found that the changes are obvious.The main manifestation was that the pores become larger,which cause the final crystals became larger.(6)In a word,the leaching mechanism of heavy metals in this experiment is gypsum erosion method.