Effect of biochar particle size on hydrophobic organic compound sorption kinetics: Applicability of using representative size

Kang, Seju,Jung, Jihyeun,Choe, Jong Kwon,Ok, Yong Sik,Choi, Yongju Elsevier 2018 Science of the Total Environment Vol.619 No.-

<P><B>Abstract</B></P> <P>Particle size of biochar may strongly affect the kinetics of hydrophobic organic compound (HOC) sorption. However, challenges exist in characterizing the effect of biochar particle size on the sorption kinetics because of the wide size range of biochar. The present study suggests a novel method to determine a representative value that can be used to show the dependence of HOC sorption kinetics to biochar particle size on the basis of an intra-particle diffusion model. Biochars derived from three different feedstocks are ground and sieved to obtain three daughter products each having different size distributions. Phenanthrene sorption kinetics to the biochars are well described by the intra-particle diffusion model with significantly greater sorption rates observed for finer grained biochars. The time to reach 95% of equilibrium for phenanthrene sorption to biochar is reduced from 4.6–17.9days for the original biochars to <1–4.6days for the powdered biochars with <125μm in size. A moderate linear correlation is found between the inverse square of the representative biochar particle radius obtained using particle size distribution analysis and the apparent phenanthrene sorption rates determined by the sorption kinetics experiments and normalized to account for the variation of the sorption rate-determining factors other than the biochar particle radius. The results suggest that the representative biochar particle radius reasonably describes the dependence of HOC sorption rates on biochar particle size.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phenanthrene sorption rate strongly depends on biochar particle size. </LI> <LI> The sorption kinetics is well described by the intraparticle diffusion model. </LI> <LI> Harmonic intensity averaged radius (<I>R</I> <SUB> <I>z</I> </SUB>) is used as a representative biochar radius. </LI> <LI> <I>R</I> <SUB> <I>z</I> </SUB> describes the dependence of sorption kinetics on biochar particle size. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of using powdered biochar and surfactant on desorption and biodegradability of phenanthrene sorbed to biochar

Kang, Seju,Kim, Geunyoung,Choe, Jong Kwon,Choi, Yongju Elsevier 2019 Journal of hazardous materials Vol.371 No.-

<P><B>Abstract</B></P> <P>The present study aimed to investigate the relationship between the desorption and biodegradability of phenanthrene sorbed to biochars by employing two approaches that may change the desorption and biodegradability: the use of powdered biochars and nonionic surfactants. Biochars derived from two feedstocks (rice husk and sewage sludge; pyrolyzed at 500 °C but showing different aromaticity) were used. When the biochars were powdered to obtain particles <250 μm the mass fractions of the desorbed phenanthrene at ∼80 days ( <SUB> f d e s </SUB> ) increased from 0.303 to 0.431 for sewage sludge biochars. On the other hand, <SUB> f d e s </SUB> for rice husk biochars remained virtually unchanged (from 0.264 to 0.255). The mass fractions of the biodegraded phenanthrene ( <SUB> f b i o </SUB> ) increased from 0.191 to 0.306 for rice husk biochars and from 0.077 to 0.168 for sewage sludge biochars. When a nonionic surfactant was added at the sub-critical micelle concentration (CMC), <SUB> f b i o </SUB> increased by 4.7 times and 8.3 times for rice husk and sewage sludge biochars. For both types of biochars, <SUB> f b i o </SUB> was larger than <SUB> f d e s </SUB> when the surfactant was added. This study suggests that the addition of nonionic surfactants can be considered if the inhibition of microbial activity is of concern in soils and sediments treated by biochar.</P> <P><B>Highlights</B></P> <P> <UL> <LI> More phenanthrene desorbs from biochar by powdering biochars or adding surfactants. </LI> <LI> Powdered biochars increases phenanthrene desorption by reducing diffusion length. </LI> <LI> Surfactants use at sub-CMC significantly enhances phenanthrene biodegradation. </LI> <LI> With surfactant, phenanthrene biodegradation has exceeded its desorption. </LI> <LI> Surfactants may facilitate microorganisms to access non-aqueous phase phenanthrene. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

열분해 온도에 따른 담뱃대 biochar의 비료학적 가치 평가

강세원 ( Se Won Kang ),서동철 ( Dong Cheol Seo ),이상규 ( Sang Gyu Lee ),서영진 ( Young Jin Seo ),박주왕 ( Ju Wang Park ),최익원 ( Ik Won Choi ),허종수 ( Jong Soo Heo ),조주식 ( Ju Sik Cho ) 한국환경농학회 2013 한국환경농학회 학술대회집 Vol.2013 No.-

우리나라에서 발생되는 농업 부산물은 해마다 증가하고 있으며, 매우 낮은 활용도를 보이고 있어 농업 부산물의 자원화 및 재활용 방안이 시급한 실정이다. 이에 본 연구는 담뱃대를 biochar로 제조하여 토양개량제로서의 활용가능성을 검토하기 위하여 열분해 온도별 (300, 500 및 700℃)로 제조된 담뱃대 biochar의 비료학적 가치를 평가하였다. 담뱃대는 경상남도 거창군 신원면에서 채 취하였으며, 단위면적 (m2)당 biomass는 430 g m-2이었다. 유기물 함량은 94.6%이었고, T-N 함량 은 1.27%이었으며, T-P 및 K2O의 함량은 각각 0.23 및 1.84%이었다. 담뱃대 biochar의 수율은 열 분해 온도가 증가될수록 biochar 수율은 감소하였으며, 이에 따른 단위면적 (m2)당 생산량은 열분 해 온도가 300, 500 및 700℃ 조건에서 각각 170, 127 및 104 g m-2이었다. 담뱃대 biochar의 열 분해 온도별로 표면 특성을 조사한 결과 열분해 온도에 상관없이 biochar의 표면은 불균일한 형태를 취하고 있었으며, 다양한 크기의 돌기들이 나타났다. 열분해 700℃ 조건에서는 표면이 녹아내 려 다른 열분해 조건에 비해 매끄러운 형태로 관찰되었다. 열분해 온도별로 제조된 담뱃대 biochar의 표면성분을 분석한 결과 열분해 온도에 상관없이 K, C, O, Mg, P, Ca 및 Si 등의 다양 한 성분이 검출되었으며, 성분비에 따른 원자량은 전반적으로 C가 가장 많았다. 담뱃대 biochar의 pH 및 EC는 열분해 온도가 증가함에 따라 점차 증가하는 경향으로 700℃ > 500℃ > 300℃이었 다. 특히 담뱃대 biochar의 EC는 열분해 700℃ 조건에서 500℃ 조건에 비해 급격히 높았다. 열분 해 온도별 담뱃대 biochar의 T-N 함량은 열분해 온도가 증가할수록 감소하는 경향으로 열분해 온 도가 300℃ > 500℃ □ 700℃ 순으로 많았다. 담뱃대 biochar의 T-P 및 K2O의 함량은 T-N 함량과 반대되는 경향으로 700℃ □ 500℃ □ 300℃ 순으로 열분해 온도가 증가할수록 T-P 및 K2O의 함 량이 증가하는 경향이었다. 이상의 결과로 미루어 볼 때 담뱃대 biochar는 비료학적으로 가치가 충분하였으나 열분해 온도에 따른 물리·화학적 특성이 다르기 때문에 이를 고려하여 토양개량제로 활용하면 농업부산물의 자원화와 재활용을 위한 하나의 방안이 될 수 있겠다.

바이오차의 시용이 채소 유묘 생장 및 양분 흡수량에 미치는 영향

홍성창,유선영,김경식,이규현,송새눈 한국환경농학회 2020 한국환경농학회지 Vol.39 No.1

. BACKGROUND: Biochar is used in various environmental fields, such as water quality and soil restoration, and affects soil fertility and nutrient cycling. Also, when crops are grown on biochar-applied soil, their characteristics may be affected. Biochar is used especially with commercial vegetable seedlings. METHODS AND RESULTS: The objective of this study was to determine the effects of biochar content in seeding mixes on early growth of lettuce (Lactuca sativa L.), Chinese cabbage (Brassica rapa L.), and red pepper (Capsicum annuum L.). Treatments consisted of a control (0: 10, ratio of biochar to seeding mixes (w/w)), 1: 9 (biochar 10%), 3: 7 (biochar 30%), 5: 5 (biochar 50%), and 7: 3 (biochar 70%). The biochar was made from risk husk and had a C/N ratio of 104. As the mixing ratio of biochar increased, pH increased whereas EC and nitrogen content decreased. The highest phosphorus content was with the treatment of 30% biochar, while there were significant increases in the weight of lettuce seedlings and concentrations of T-N, P2O5, K2O, MgO, and Na with the treatments of 30% and 50% biochar. Although the weight of Chinese cabbage seedlings increased with the treatment of 10% biochar, the increase was not statistically significant. Also, there was an increase in the weight of red pepper seedlings with the treatment of 30% biochar, but the increase was not statistically significant. With increases in the biochar mixing ratio, the K2O concentration of red pepper seedlings increased, but the concentrations of P2O5, CaO, MgO, and Na decreased. It was believed that this was because of absorption inhibition by calcium-phosphate formation in the seeding mixes owing to increased pH. CONCLUSION: In conclusion, adding biochar to seeding mixes is considered to be an important mean for growing healthy vegetable seedlings. More field experiments are needed to verify the effect of biochar on vegetable crop growth over the entire growing season.

전기 Biochar 제조장치에서 제조된 과수전정지 Biochar의 화학적 특성

박종환 ( Jong Hwan Park ),김성헌 ( Seong Heon Kim ),서동철 ( Dong Cheol Seo ),조주식 ( Ju Sik Cho ),허종수 ( Jong Soo Heo ) 한국환경농학회 2013 한국환경농학회 학술대회집 Vol.2013 No.-

우리나라 과수 재배면적은 81천ha으로 단위 면적당 과수전정지 발생량은 1,742 kg 10a-1이며, 연 간 발생량은 1,411천톤으로 농업부산물 중 볏짚 다음으로 많이 발생된다. 이러한 과수전정지 중 잔가지는 파쇄하여 퇴비로 사용하며, 굵은 가지는 땔감으로 사용하거나 또는 과수원 내에 방치하고 있는 실정이다. 이에 과수전정지의 활용도를 높이면서 동시에 농업 및 환경정화제로 이용가능 한 biochar가 대두되기 시작하였다. Biochar는 혐기적 조건에서 열분해를 통해 얻은 숯으로 많은 연구진에 의해 탄소격리, 온실가스 저감, 토양개량제로서 효과 등이 구명되고 있다. 본 연구는 배, 복숭아, 사과 및 단감 재배포장에서 과실의 수확이 끝난 뒤 전정 작업을 통해 수거된 과수전정지 를 전기가열형 biochar 장치에서 열분해 온도 및 시간을 600℃, 6시간으로 조절하여 저속열분해 하였으며, 제조된 biochar의 수율, 무기성분 특성을 조사하였다. 과수전정지 종류별 제조된 biochar 의 수율은 사과나무 (22.46%) > 감나무 (25.25) > 배나무 (20.28%) > 복숭아나무 (18.86%)순으로 사과나무 및 감나무가 가장 높았다. 과수전정지 종류별 biochar의 pH는 원재료에 비해 증가하는 경향이었으며, 배나무, 복숭아나무, 사과나무, 감나무 원재료의 EC는 1.12, 0.95, 0.84, 1.04 dS m-1 인데 비해 열분해 후 EC는 14.7, 26.2, 12.8, 17.5 dS m-1로 급격히 증가하는 경향이었다. 과수전 정지 종류별 biochar의 T-N 함량은 원시료에 비해 증가하는 경향이었고, 과수전정지 종류별로 비 교했을 때 배나무가 1.47%로 가장 높았으며, 사과나무가 0.49%로 가장 낮은 함량을 보였다. 과수 전정지 종류별 T-P 함량은 별 다른 차이 없이 1.25-1.74% 범위였다. 과수전정지 종류별 biochar의 K의 함량은 원시료 0.13-0.35% 범위에서 열분해 후에는 0.93-1.25%의 범위로 증가하는 경향이었으며, Ca의 함량도 K와 동일한 경향이었으며, 복숭아나무에서 1.41%으로 가장 높았고, 배나무가 0.91로 가장 낮았다. 과수 전정지 종류별 Mg의 함량은 사과나무에서 2,011 mg kg-1이었으며, 사과 나무를 제외한 전정지의 경우는 1,745-1,790 mg kg-1의 범위로 별 차이 없었다. 이상의 결과를 미루어 볼 때, 전기가열식 열분해 과정을 통해 생산된 과수전정지 biochar는 다량의 무기성분 함유하고 있었으며, 특히 농업적으로 이용시 화학비료의 절감 효과를 기대할 수 있을 것이라 판단된다.

Consecutive reduction of Cr(VI) by Fe(II) formed through photo-reaction of iron-dissolved organic matter originated from biochar

Kim, Hye-Bin,Kim, Jong-Gook,Kim, Seon-Hee,Kwon, Eilhann E.,Baek, Kitae Elsevier Applied Science Publishers 2019 Environmental pollution Vol.253 No.-

<P><B>Abstract</B></P> <P>Employing biochar for environmental remediation has been widely practiced. Nonetheless, the reduction mechanisms of hexavalent chromium (Cr(VI)) in the presence of biochar have not been fully elucidated (<I>i.e.,</I> direct or indirect reduction of Cr(VI) by biochar). In particular, the effect of light on Cr(VI) reduction by biochar was rarely reported. Thus, to clarify the reduction mechanisms of Cr(VI) by biochar at the fundamental level, this study laid great emphasis on the photo-induced reduction of Cr(VI) in the application of biochar. Biochar releases dissolved organic matter (DOM), the DOM can extract Fe(III) from soil by complexation, and the complexes can be photo-reacted under the light. In these respects, Fe(II) formed by the photo-induced reaction of DOM-Fe(III) was particularly evaluated in this study. To evaluate that, three biomass samples (rice straw, granular sludge from an up-flow anaerobic sludge blanket, and spent coffee ground) were torrefied to biochar. To circumvent the adsorption of Cr(VI) onto biochar, biochar extractives (served as a source for DOM) and Fe(III) solution were tested with/without UV light to prove Fe(II) formation. This study experimentally proved that the more Fe(II) under the UV radiation was formed in the co-existence with biochar extractives and Fe(III). All experimental data from three biochar samples were indeed very similar. Cr(VI) reduction by Fe(II) from GB, RB, and CB reached up to 96, 79, and 100%, respectively. The different reduction efficiency signified that the low molecular weight of organic acids, such as oxalate, were more sensitive to the UV light, thereby resulting in the enhanced Fe(II) formation. Such Fe(II) formation subsequently led to the high reduction efficiency of Cr(VI).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Biochar application increases significantly the reduction of Cr(VI) under the light condition. </LI> <LI> A reductant Fe(II) was transformed via photoreaction of DOM-Fe (III) complexes. </LI> <LI> Photo-induced indirect reduction is a major mechanism of Cr(VI) reduction by biochar. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Application of two contrasting rice-residue-based biochars triggered gaseous loss of nitrogen under denitrification-favoring conditions: A short-term study based on acetylene inhibition technique

Malghani, Saadatullah,Kim, Jinhyun,Lee, Seung-Hoon,Yoo, Ga-young,Kang, Hojeong Elsevier 2018 Applied soil ecology Vol.127 No.-

<P><B>Abstract</B></P> <P>Denitrification is the key microbial process that leads to gaseous loss of soil nitrogen in agricultural lands. Most alarmingly, the dominant gas species could be N<SUB>2</SUB>O, which is a much stronger greenhouse gas than CO<SUB>2</SUB>. In addition to the primary role as tool for soil carbon sequestration, biochar has the potential to suppress N<SUB>2</SUB>O emissions. However, the mechanism for the suppression of N<SUB>2</SUB>O emissions by biochar remains elusive. To address this, we performed a short-term incubation experiment targeting the impact of two contrasting biochars on gaseous loss of soil N under denitrification-favoring conditions including high load of NO<SUB>3</SUB> <SUP>−</SUP> (100 µg N/g soil), anoxia and high moisture content (70% WFPS). The acetylene inhibition technique was adopted to differentiate N losses as N<SUB>2</SUB> and N<SUB>2</SUB>O. Two biochars produced from rice chaff (600 °C, pH > 10, C:N 70) or rice husk (300 °C, pH < 5, C:N 54) were applied at two rates (5 and 10% w/w). Results exhibited an increase in gaseous loss of N in all biochar treatments compared with an unamended control. The presence of a positive correlation between total denitrification and CO<SUB>2</SUB> emission rates suggested that biochar derived labile carbon played a pivotal role in triggering the loss of N in gaseous forms. Similarly, the abundances of denitrifying genes <I>nosZ</I> and <I>nirS</I> were considerably higher in biochar treatments, indicating denitrifier’s heterotrophic nature. The biochar pyrolysis conditions and application rates played a decisive role in controlling N<SUB>2</SUB>O emissions. Rice chaff biochar, primarily characterized by its alkaline pH, significantly suppressed N<SUB>2</SUB>O emissions. Taken together, biochar amendment to agricultural soil can trigger N losses via denitrification and only the alkaline biochar suppressed N<SUB>2</SUB>O emissions, probably because of the enhanced activity of N<SUB>2</SUB>O reductase.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We recorded an increase in gaseous loss of N after application of rice base biochars. </LI> <LI> The abundance of denitrifying genes <I>nosZ</I> and <I>nirS</I> were higher in biochar treatments. </LI> <LI> Biochar addition to soil triggered rates of denitrification process. </LI> <LI> Soils treated with alkaline biochar had the lowest N<SUB>2</SUB>O emissions. </LI> </UL> </P>

몇가지 채소 유묘의 초기생장과 양분함량에 미치는 바이오차 효과

홍성창 ( Hong Sung-chang ),최순군 ( Chio Soon-kun ),최동호 ( Choi Dong-ho ),허승오 ( Hur Seung-oh ),신중두 ( Shin Jung-do ),장은숙 ( Jang Eun-suk ) 한국환경농학회 2018 한국환경농학회 학술대회집 Vol.2018 No.-

Carbon sequestration, amendment on green house gas emission, and soil remediation can enhanced by the biochar. Biochar effects on soil fertility and nutrient cycling. Crops growing on the biochar applied soil could be affected on its characteristics. There are many seeding mixes for a lot of vegetable seedling. The objective of this study was to investigate the effects of biochar contents of seeding mixes on early growing of lettuce (Lactuca sative) and red pepper (Capsicum annunm), The consist of treatments were control(0 : 1, biochar ratio to seeding mixes (w/w)), 1 : 9(10%), 3 : 7 (30%), 5 : 5 (50%), and 7 : 3 (70%), respectively. The pH of mixed substrates were increased from 5.5 (control) to 8.3 (biochar 70%) depending on biochar contents, while the EC were decreased from 2.1 (control) to 0.8 (biochar 70%). As the biochar content increased in the mixed substrate, the T-N and K content were decreased. The plant length, leaf number, and dry weight of lettuce and red pepper were in order of 50%, 30%, 10%, control, and 70%. These characteristics of lettuce and red pepper seedling showed significantly differences. Increasing content of biochar (10%, 30%, and 50%) progressively activate growing of the lettuce and red pepper but at 70% treatment growing of these were retarded. As the biochar content in the mixed substrate increased T-N, P, K, Mg, and Na content of lettuce, 30 days after sowing, were increased, but Ca content not showed differences. 80 days after sowing red pepper seedling showed different nutrient content compared to those of lettuce seedling. The content of K of red pepper seedling increased depending on the biochar content but the content of P, Ca, and Mg were decreased. On the point of view nutrient content of seeding mixes, at the 50% treatment plot, the amount of nitrogen was 80% of the control, but fresh weight of the lettuce and red pepper were most heavy. Thus, it was assumed that early growing of the lettuce and red pepper seedling were affected by the action of biochar that adsorption and holding nutrient reaction in seeding mixes. In conclusion, adding the biochar to seeding mixes was considered as an important measures for growing healthy seedling and carbon sequestration. More field experiments are needed to verify the biochar effect of crop growth over the entire growing season.

Effects of different biochar amendments on carbon loss and leachate characterization from an agricultural soil

Yang, Xing Ya,Chang, Kwang-Hyeon,Kim, You Jin,Zhang, Jin,Yoo, Gayoung Elsevier 2019 CHEMOSPHERE - Vol.226 No.-

<P><B>Abstract</B></P> <P>Selection of an appropriate biochar as a soil amendment requires a thorough investigation of the effects on soil ecosystems and adjacent water systems via leaching. Different biochar characteristics influence retention or leaching of different soil and biochar components. A lab lysimeter study was conducted to investigate carbon (C) balance and leachate quality with biochar additions. Biochar made from wood pellets (WP) and sewage sludge (SS) produced at 400 °C (WP400 and SS400) and 700 °C (WP700 and SS700), respectively, were applied to silt loam soil at an application rate of 4%. Fluorescence excitation-emission spectrophotometry (EEMs) was utilized to understand the compositional changes in leachate dissolved organic carbon (DOC). Our results show that DOC contributed the largest portion of C leaching loss. The WP treatments increased DOC mass loss, but did not significantly change leachate DOC quality. SS400, in comparison, increased mass loss of DOC and SS700 decreased it probably due to its higher adsorptive capacity to DOC. Unlike WP treatments, SS treatments significantly changed leachate DOC quality. Chemical oxygen demand (COD) was reduced with SS400 and SS700 biochar additions, which is assumed to be related to SS biochar's high oxygen-containing surface functional groups. Reduction in total nitrogen (TN) leaching by WP700 and SS700 treatments might be related to the higher micropore surface area. Over all, our findings imply that changes in the different components of the leachate from biochar-amended soil are related to different biochar properties, such as labile matter content, total surface area, micropore volume and cation exchange capacity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> DOC contributed the largest portion of C leaching loss from biochar added soils. </LI> <LI> Leachate properties of biochar addition were related to biochar characteristics. </LI> <LI> Wood pellet biochar increased DOC leaching but did not influence DOC quality. </LI> <LI> Sewage sludge biochar (700 °C) reduced COD/TN leaching and retained humic substances. </LI> </UL> </P>

Heavy metal removal from aqueous solutions using engineered magnetic biochars derived from waste marine macro-algal biomass

Son, Eun-Bi,Poo, Kyung-Min,Chang, Jae-Soo,Chae, Kyu-Jung Elsevier 2018 Science of the Total Environment Vol.615 No.-

<P><B>Abstract</B></P> <P>Despite the excellent sorption ability of biochar for heavy metals, it is difficult to separate and reuse after adsorption when applied to wastewater treatment process. To overcome these drawbacks, we developed an engineered magnetic biochar by pyrolyzing waste marine macro-algae as a feedstock, and we doped iron oxide particles (e.g., magnetite, maghemite) to impart magnetism. The physicochemical characteristics and adsorption properties of the biochar were evaluated. When compared to conventional pinewood sawdust biochar, the waste marine algae-based magnetic biochar exhibited a greater potential to remove heavy metals despite having a lower surface area (0.97m<SUP>2</SUP>/g for kelp magnetic biochar and 63.33m<SUP>2</SUP>/g for hijikia magnetic biochar). Although magnetic biochar could be effectively separated from the solution, however, the magnetization of the biochar partially reduced its heavy metal adsorption efficiency due to the biochar's surface pores becoming plugged with iron oxide particles. Therefore, it is vital to determine the optimum amount of iron doping that maximizes the biochar's separation without sacrificing its heavy metal adsorption efficiency. The optimum concentration of the iron loading solution for the magnetic biochar was determined to be 0.025–0.05mol/L. The magnetic biochar's heavy metal adsorption capability is considerably higher than that of other types of biochar reported previously. Further, it demonstrated a high selectivity for copper, showing two-fold greater removal (69.37mg/g for kelp magnetic biochar and 63.52mg/g for hijikia magnetic biochar) than zinc and cadmium. This high heavy metal removal performance can likely be attributed to the abundant presence of various oxygen-containing functional groups (COOH and OH) on the magnetic biochar, which serve as potential adsorption sites for heavy metals. The unique features of its high heavy metal removal performance and easy separation suggest that the magnetic algae biochar can potentially be applied in diverse areas that require biosorbents for pollutant removal.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic biochar derived from marine macro-algae was made for heavy metal adsorption. </LI> <LI> Physicochemical properties and isotherms were characterized using various techniques. </LI> <LI> Iron-loaded condition was optimized for Cd, Cu, and Zn removal and magnetic separation simultaneously. </LI> <LI> Magnetic macro-algae biochar had high selectivity for Cu with plentiful O-containing groups. </LI> <LI> Adsorption and recovery ability showed an opposite tendency as iron doping increased. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>