Removal of metal impurities in rice husk and characterization of rice husk ash under simplified acid pretreatment process

Abstract

Acid pretreatment plays an important role in the preparation of amorphous silica with high activity and high specific surface area before combustion process. However, some limitations and problems exist in the pretreatment process of previous literatures. On the basis of this, this work is aimed at simplifying the acid pretreatment process and combustion condition, which could present a more advantageous process for practical industrial applications. Then the removal percentage and behavior of metal impurities in rice husk is studied by ICP‐OES, and effects of acid pretreatment on properties of rice husk ash (RHA) at various combustion temperatures are comprehensively investigated in comparison with previous results by scanning electron microscope (SEM), X‐ray fluorescence (XRF), X‐ray diffractometer (XRD), and surface analyzer. The results suggest that the removal degree of each metal is various due to each chemical form in rice husk, of which removal percentage of K is especially remarkable. The contributions of simplified acid pretreatment to the properties of RHA are equally prominent: smaller nanoscale particles, higher purity, and specific surface area of above 200 m2/g. In addition, the pretreatment can also eliminate the crystallization and keep the high activity of RHA in combustion temperature range of 600–900°C. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 830–837, 2017

Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies—A Review

“…By increasing the CT, carbon content and silica purity remain around the same until SiO 2 crystallization takes place [19,20,69]. On the other hand, higher CT and RT reduce specific surface area (SSA) and total pore volume of RHA [19,71]. Often, this is attributed to the reduction in the carbon content and ash agglomeration, resulting in diminished porosity [189].…”

“…Often, this is attributed to the reduction in the carbon content and ash agglomeration, resulting in diminished porosity [189]. According to Table 3, close to 600 • C, SSA and pore volume strongly depend on the CT, and they drastically decrease by increasing CT from 600 to 700 • C or above [19,71]. Therefore, to produce high quality silica, it seems that the optimum CT for combustion of untreated RH is around 600 • C. The quality of the resulting biogenic silica also depends on the combustion technology [179,190].…”

“…Since RH and RS are composed of organic matter such as cellulose, hemicellulose, and lignin as well as inorganic matter [50,53,91], washing or leaching the fuel samples with specified chemical solutions can alter the organic and inorganic composition of RH and RS as well as the composition of resulting RHA and RSA. Ash-forming elements can be divided into water soluble, acid soluble and insoluble parts [71,196,197]. In general, alkali metals (potassium, sodium) belong to the water soluble portion of the ash while alkaline earth metals (calcium, magnesium) and manganese are acid soluble.…”

“…Summary of fuel washing strategies for RH and RS used in Figure 4 [102,105,109]. Another advantage of fuel pre-treatment is that it can reduce the risk of crystallization in the resulting biogenic silica [67,71,187,189,199]. Pre-treated RHs remained amorphous up to 1000 • C [200].…”

“…Furthermore, uncontrolled open burning of these materials produces crystalline ash with high emissions [59], which is well recognized as a lung carcinogen as well as the health risk from silicosis caused by silica deposition in the lung tissue [60,61]. To overcome these issues, researchers have been investigated feasible, economical, and environmentally friendly strategies to convert RH and RS into pure biogenic silica via combustion based on various scientific publications [53,54,[62][63][64][65][66][67][68][69][70][71][72][73] and patents [74].…”