Process for producing heavy-metal-mediated biochar complex cured by using silicate
A process for producing a heavy metal mediated biochar composite using silicate solidification. Hydrocharis dubia has excellent enrichment of manganese ions in sewage, and is used to treat sewage water to adsorb heavy metals such as lead, manganese and zinc contained in the sewage water into roots, stems and leaves thereof, which are pyrolysed in stages at high temperature with activated red mud and bentonite prior to blending with zeolites, to produce said heavy metal mediated biochar composite; the process significantly extends the migration time of heavy metals, increases the stability of heavy metals and reduces the risk of environmental pollution by heavy metal leakage.
1 . A process for producing a heavy metal mediated biochar composite, comprising the following steps of:
step 1, preparing a heavy metal-based biomass by enriching an aquatic plant with heavy metals in sewage water; said heavy metal elements comprise lead, manganese and zinc;
step 2, pyrolyzing said heavy metal-based biomass produced in step 1 together with a silicate-containing composite comprising red mud and bentonite to obtain a pyrolysis product, wherein the pyrolyzing is completed in three stages:
first stage: the pyrolysis temperature is 200-350° C., the heating rate is 6-12° C./min, and the holding time is 0.5-2 h;
second stage: the pyrolysis temperature is 360-450° C., the heating rate is 7-13° C./min, and the holding time is 0.5-3 h;
third stage: the pyrolysis temperature is 460-600° C., the heating rate is 5-10° C./min, and the holding time is 1-4 h; and
step 3, modifying zeolites with a strong acid, and mixing the modified zeolites with the pyrolysis product of step 2 to yield the heavy metal mediated biochar composite.
2 . The process according to claim 1 ,
wherein said aquatic plant includes any one or more of emergent plants, floating leaf plants, submerged plants, and floating plants.
3 . The process according to claim 2 , wherein submerged plant is one or more selected from the group consisting of bitter grass, Hydrocharis dubia and Potamogeton malaianus.
4 . The process according to claim 2 , wherein said aquatic plant enriched with heavy metals is dried at 80-160° C. for 0.5-5 h to obtain said heavy metal-based biomass.
5 . The process according to claim 4 , wherein in step 1, the concentration of lead is 100-400 mg/L, the concentration of manganese is 400-800 mg/L, and the concentration of zinc is 200-600 mg/L, in said sewage water.
6 . The process according to claim 1 , wherein a dry weight ratio of said heavy metal-based biomass, said red mud and said bentonite is 1:(0.2-5):(0.1-3).
7 . The process according to claim 1 , wherein in step 2, said red mud is mixed under stirring with a dried heavy metal-based biomass obtained from step 1 for 2-12 h, and then is activated by oven drying at 60-200° C., thereafter is grounded and sieved through 60-120 mesh screen.
8 . The process according to claim 7 , wherein in step 2, a mixture of the ground-sieved red mud and said heavy metal-based biomass is added to said bentonite having a water content of 30% to 60%, and stirred for 10 to 48 h.