The use of biochar as a soil amendment attracts increasing research interest. However, the lack of methods to detect and monitor biochar in situ limits the validation of the field-scale application of biochar. Spectral induced polarization is a potential tool to characterise biochar in soil. The aim of this study is to investigate the sensitivity of spectral induced polarization to biochar in sand and to understand how the physicochemical properties of both the biochar and the surrounding matrix influence the spectral induced polarization response. To this end, spectral induced polarization measurements were conducted on four types of biochar with different mass fractions disseminated in saturated sand as a host media with changing electrical conductivity. In addition, it was investigated how the spectral induced polarization response depends on the particle size of biochar. The measured SIP data were interpreted by Debye decomposition to obtain values for the peak relaxation time, τ peak ; total chargeability, M; and normalised total chargeability, M n . Spectral induced polarization showed a clear and specifically differentiated response to the presence of all four types of biochars. M was found to be proportional to the mass fraction of biochars, although relationships varied for each type of biochars. τ peak of biochars increased with increasing particle size. Increased electrolyte concentration enhanced M n for all biochars, although again, the specific response was different for each biochar. In addition, higher electrolyte concentrations decreased τ peak for biochars derived from wood through pyrolysis but did not affect τ peak of biochar derived from miscanthus through hydrothermal carbonisation. It was concluded that the spectral induced polarization response of pyrolytic biochars resembled that of conductors or semiconductors, whereas the spectral induced polarization response of hydrothermal carbonisation biochar more closely resembled that of clay. Overall, the findings in this study suggest that spectral induced polarization is a promising method for the detection and characterisation of biochar in soil.

Core Ideas Water retention and spectral induced polarization were measured for biochar in sand. Water retention curves could be fitted by using a dual porosity model. Residual water content was found to increase with the addition of biochar. The polarization of sand–biochar mixtures was much larger than that for sand. Spectral induced polarization may be suitable for monitoring biochar in the field. Biochar is considered a promising soil amendment, but an effective method to detect and characterize the spatial distribution and temporal dynamics of biochar in soil is still missing. The aim of this study is to investigate the ability of the spectral induced polarization (SIP) method for the noninvasive detection of biochar in unsaturated sandy media. In particular, a pure sand and two sand–biochar mixtures with 1 and 2% biochar made from pine (Pinus spp.) wood by pyrolysis at 800°C were investigated. The measured SIP spectra as a function of saturation were interpreted by fitting a Cole–Cole model to the low‐frequency part of the SIP measurements. The porous nature of the biochar particles strongly affected the SIP response of the partially saturated sand–biochar mixtures. Due to the high residual water content of the biochar in a dry background, the relationship between bulk electrical conductivity and water saturation was nonlinear in a log–log representation. This nonlinear behavior could adequately be explained with a dielectric mixing model that considered the drainage of the biochar particles. Both the measured phase and chargeability of the sand–biochar mixtures showed a complex dependence on water saturation. This was attributed to the decrease in polarization strength of the biochar particles with desaturation and the simultaneous increase in phase of the sand background. Overall, the results of this study suggest that field SIP measurements may be a promising tool for the characterization and monitoring of biochar amendments to agricultural soils.

In order to obtain optimized operating condition for industry naphthalene purification using fractional crystallizing method, the influence of heating rate, crystallizing times, holding time and cooling rate on the yield and purity of industrial naphthalene were studied. The industrial naphthalene from AISC Chemical General tar workshop was used as starting material in the study. The results show that the yield and purity of refined naphthalene can achieve 94.2％ and 99.30％ respectively, when the heating rate is 1.2°C/h, the cooling rate is 3°C/h, holding time is 5 hours and the crystallizing times is 3. The result of present study provides a theoretical foundation for the actual production and technology improvement of naphthalene purification.