Preliminary Study On Physical And Chemical Properties Of Biochar And Its Quality Evaluation Methods

The study of biochar is the basis of biochar and the way to evaluate biochar is the key to biochar application.Due to the wide variety of biochar and the different carbonization process,the physical and chemical properties of biochar are obviously different.In order to meet the needs of agricultural application better,it is necessary to classify and evaluate biochar.In this study,In this study,common waste biomass such as peanut hulls,rice straw,corn stalks and sorghum stalks were used as raw materials,72 kinds of biochars with different physicochemical properties were prepared under different carbonization conditions.whose physical and chemical indicators such as carbon content,pH,nutrient,specific surface area,pore size,pore volume and heavy metal content were measured.The effects of biomass feedstock and carbonization process on the physical and chemical properties of biochar were analyzed,and the classification and evaluation of biochar were attempted to provide a reference for the construction of a comprehensive evaluation method for biochar product quality.The main findings are as follows:(1)With the increase of carbonization temperature,the content of biochar fixed carbon,organic carbon,the inorganic carbon,total carbon,pH,total nitrogen,available phosphorus and available potassium,specific surface area and pore volume increased,and heavy metal content of chromium,arsenic,lead increased,while the pore size and heavy metal content of cadmium decreased.(2)Biomass raw materials and carbonization process are important factors affecting the physical and chemical properties of biochar.Among them,biomass raw materials have the most significant influence on the physical and chemical properties of biochar,followed by carbonization temperature and reactivity time.(3)The results of clustering analysis showed that the main physical and chemical indexes of biochar can be divided into two levels.Among them,organic carbon content is divided into 70%-80% and 40%-70%.The pH is divided into two grades: 10.5-12 and 9-10.5;The nitrogen content was divided into 1.4% to 1.7% and 1% to 1.4%.The content of available phosphorus was divided into two levels: 1600mg/kg-3000mg/kg and 900mg/kg-1600mg/kg.The available potassium content was divided into 40g/kg-85g/kg and 14g/kg-40g/kg.(4)The heavy metal content of all biochar prepared in this study was within the range stipulated of the standard "NY/T 3041-2016 Biochar base fertilizer ".Among them,the arsenic content was divided into three levels: 3-20μg/kg,20-55μg/kg,and 55-90μg/kg.The content of cadmium is divided into two levels: 2-7μg/kg and 7-11μg/kg.The lead content is divided into 40-105μg/kg and 105-200μg/kg.The chromium content can be divided into two grades: 250-600μg/kg and 600-1300μg/kg.(5)According to the clustering results,each index was normalized and the score was assigned to the scale,and the heavy metal was negative,and the biochar quality was evaluated.The results showed that there were significant differences in biochar composite scores of different materials.The comprehensive score of high carbon content of straw was higher,and the overall biochar score of peanut shell was lower.The overall score of peanut shell biochar was higher when the carbonization temperature was 400℃ and 900℃,simultaneously the residence time was 60 minutes.Rice straw biochar has a higher comprehensive score at a carbonization temperature of 600℃ and a residence time of 60 minutes.The corn straw biochar has a higher comprehensive score when the carbonization temperature is ≥700℃ and the residence time is 30 minutes.Sorghum straw biochar has the highest comprehensive score when carbonization temperature is 600℃,700℃ and residence time is 30 min.