Preparation and use of slow-release iron-based biochar soil heavy metal passivator

A method for preparing a slow-release iron-based biochar soil heavy metal passivator, characterized by comprising the steps of:

• (1) drying a biomass in the air and crushing the same, increasing the temperature to 300° C. to 800° C. under the conditions of air isolation, and keeping this temperature for 3 to 12 hours to prepare the iron-based biochar precursor;
• (2) formulating a ferric salt or ferrous salt into a solution of an iron content of 0.5% to 5% by mass;
• (3) to the iron-based biochar precursor prepared in step (1) adding, under stirring, the iron-containing solution prepared in step (2) under the conditions of keeping the temperature at 80 to 350° C., the mass ratio of the iron-based biochar precursor to the iron-containing solution is 1:0.2 to 1:5;
• after having been stirred until uniform, cooling the mixture to room temperature, drying, crushing and sieving to prepare the iron-based biochar material;
• (4) mixing the iron-based biochar material prepared in step (3), kaolin and bio-starch at 100:
• 0.5:1 to 100:5:10 by weight part, until uniform, adding water or spraying water under stirring to a water content of 50% to 80%, and then drying to obtain the core material;
• (5) adding a chitosan solution into an acidic silica sol at 55-75° C. under the stirring conditions to control the volume ratio of the chitosan solution to the acidic silica sol to 1:2 to 1:5, after the completion of the addition, heating the same at 55-75° C. for 0.5-1 h to obtain an acidic coating material precursor;
• adding an emulsifier to the prepared acid coating material precursor under stirring at 55-75° C., wherein the emulsifier is control in an amount of 0.5% to 5% of the chitosan, stirring until uniform, then adding an alkaline catalyst for catalysis, and keeping the conditions of 55 to 75° C. under stirring for 1 to 1.5 h, controlling the pH to 9 to 11;
• removing bubbles by vacuum, to prepare an alkaline coating material;
• (6) coating the core material prepared in step (4) with the alkaline coating material prepared in step (5), and controlling the mass volume ratio of the core material to the alkaline coating material to 30:1 to 5:1, and drying the coating in the air to obtain a slow-release iron-based biochar soil heavy metal passivator.