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The selection of "high-purity calcium hydroxide" cannot be based solely on the Ca(OH)₂ content figure. For industrial users, the true value of high purity lies in: the main components meeting process requirements, controlled impurities related to the application, consistent testing methods and results, and stable delivery across continuous batches. Comparing only the highest values on promotional materials easily overlooks the actual impact of carbonates, moisture, insoluble matter, iron, and other elements.
This article focuses on the calcium hydroxide products and domestic alternative applications of Dongguan Hanwei Technology Co., Ltd. (hereinafter referred to as "Hanwei Technology"), answering core questions in the procurement of high-purity calcium hydroxide: how to interpret the content, how to determine impurities, how to compare reports, how to verify samples, and why high purity does not necessarily equate to compatibility.
Chemically, calcium hydroxide has the formula Ca(OH)₂. However, industrial products are not isolated symbols existing outside the production process. Raw materials, calcination, digestion, grading, impurity removal, packaging, and storage all affect the final result. There is no universally applicable procurement list for "high purity" that covers all applications; therefore, companies cannot judge the grade solely based on the product name.
A more practical definition is: under agreed-upon testing methods, the main Ca(OH)₂ content meets the company's requirements, while key impurities, physical state, and batch fluctuations are within acceptable ranges. This definition includes four elements: agreed-upon method, main content, application-related impurities, and stability. Lacking any one of these, "high purity" may simply be an unenforceable description.
For example, an application may only require neutralization capacity and low residue, where whiteness may not be a primary concern; another light-colored formulation, even with a high content, may still fail if there are significant iron or color fluctuations; some continuous processes are more concerned with particle size, wettability, and actual utilization. High purity must be interpreted within the specific application context.
Before comparing contents, the project name and method should be confirmed. The report may directly state the calcium hydroxide content, or it may calculate the content after testing for available calcium, or it may use titration or other methods to obtain the result. Other alkaline components in the sample, the degree of carbonation, the water content, and the pretreatment method can all affect the results. If both suppliers list "content," but the methods are different, the numbers may not be directly comparable.
The current HG/T 4120—2024 "Industrial Calcium Hydroxide" is the industry product standard for industrial calcium hydroxide, and it replaced the 2009 version on May 1, 2025. If the procurement documents cite this standard, the version year should be specified, along with the company's specific limits and the actual testing method; simply stating "compliant with industry standards" while omitting the content, impurities, methods, and batch results that are truly important for high-purity projects is insufficient.
At least five points should be asked during procurement: What is the testing basis? Are the results expressed on a dry basis or in other states? Is the specification a lower limit, range, or typical value? Do the decimal places in the report represent the true testing accuracy? Are the company's retesting methods consistent with the supplier's methods? For domestic substitution, the same method should be used to test both currently used imported samples and candidate domestic samples.
Content figures also need to be understood in conjunction with time. Calcium hydroxide may absorb carbon dioxide and form calcium carbonate upon contact with air; packaging sealing, sampling exposure, and storage time can affect the sample's condition. Therefore, samples should be labeled with the batch number, production date, and sampling time; retest results after opening the bag cannot be simply equated with the factory condition.
Impurities should be identified based on application risk, not simply by increasing their quantity. Common areas of concern include iron, magnesium, silicon, aluminum, insolubles, carbonates, moisture, and certain heavy metals, but the focus varies depending on the product and process. Companies can first analyze currently used, qualified products and then determine a long-term control list based on failure risks.
Iron is often associated with base color, hue, and metal-sensitive processes. Reports may use Fe or Fe₂O₃, and consistency in terminology is crucial. Elements such as magnesium, silicon, and aluminum may originate from raw materials or processes and affect certain reactions, filtration, and residues, but absolute judgments cannot be made without considering the application. Insolubles can help identify some residue risks but cannot account for all hard particles and foreign matter issues.
Carbonates deserve separate attention because they may be related to the state of raw materials, digestion processes, and subsequent absorption of carbon dioxide from the air. Companies need to determine whether changes in carbonates affect the active ingredient, reaction rate, residues, or final product, rather than simply treating it as a supplementary item in the report.
For projects that are particularly sensitive to impurities, a relatively complete elemental analysis can be performed during the introductory phase to establish an "impurity fingerprint" between the imported benchmark and domestic candidate samples. Subsequently, only items confirmed to be risky, detectable, and requiring long-term control should be included in the procurement specifications. This approach is more economical and targeted than indiscriminately adding testing items.
High purity describes the levels of major components and impurities; high whiteness describes optical appearance; low iron describes a specific type of impurity; and ultrafine describes particle size characteristics. These four terms may appear simultaneously on a product, but they are not interchangeable.
A high-purity product containing small amounts of colored impurities or differences in particle size causing light scattering may not necessarily have higher whiteness; a high-whiteness product can achieve a good appearance through raw materials and processes, but this does not mean all impurities are lower; low iron only indicates that iron is under strict control, not that magnesium, silicon, aluminum, or insoluble substances are present; very fine particle size does not improve chemical purity and may even lead to agglomeration, moisture absorption, and transportation problems.
Purchase specifications should break down these indicators. Specify only what the company needs; unnecessary items can be observed but should not have overly strict limits. Piling all marketing terms together often increases costs without necessarily improving process results.
The Product Data Sheet (TDS) typically describes product positioning, specification range, typical properties, packaging, and recommended uses, suitable for pre-screening of models. The Certificate of Account (COA) corresponds to a specific batch, suitable for determining whether a batch of products meets release criteria. Purchasing should not use typical TDS values to replace individual COAs, nor should a single, well-performing COA be used to infer long-term capability.
When reading a TDS, distinguish between typical and guaranteed values, check if the testing methods are specified, and confirm the truly different items between different models. When reading a COA, verify the product model, batch number, production date, testing date, items, limits, results, units, and issuance information. If the report only has results without specifications, it's difficult to determine the release logic; if items frequently change between batches, verify consistency in quality management.
Companies can put currently used imported products, Hanwei Technology's candidate models, and internal requirements in the same table, but units and methods must be standardized first. For indicators that cannot be directly converted, retesting should be performed, rather than artificially piecing together two reports into a seemingly complete comparison table.
The first step is to define the intended use. Clearly state the role, dosage, contact medium, temperature, feeding and mixing methods of calcium hydroxide in the process, as well as the current problems to be solved. The objective could be to reduce impurities, stabilize color, reduce residue, improve reaction utilization, or replace imports, but it must be measurable.
The second step is to establish a baseline. Continuously sample existing qualified products to obtain main content, key impurities, particle size, moisture, whiteness, or other necessary data, and record the corresponding production results. The baseline should represent the daily stable state, not a single best performance.
The third step is data pre-screening. Obtain the latest TDS, COA, SDS, and packaging information for candidate models, excluding products with unclear testing specifications, missing batch data, or significant discrepancies in key indicators.
The fourth step is retesting using the same method. Test the imported baseline and domestic samples by the same laboratory to reduce bias caused by methods and instruments. When results approach the limits, repeat testing should be performed, and measurement uncertainty should be assessed.
The fifth step is application validation. Conduct small-scale tests according to the actual formula and process, recording the reaction, dispersion, filtration, residue, color, equipment status, and final performance. If necessary, proceed to pilot-scale or production line trials; do not rely solely on powder testing.
The sixth step is multi-batch validation. After the sample passes, continue validating multiple normal production batches, and incorporate the final requirements into the procurement specifications and quality agreement. Only after this stage is completed can the stability of the supply be determined.
High-purity products often require stricter raw material and process control, which may lead to corresponding price variations. Whether it's worthwhile to use them should be determined by comparing their impact on unit consumption, finished product yield, residue, cleaning, filtration, and downtime risks.
If increasing the purity reduces the actual dosage, decreases post-processing burden, or improves finished product stability, a higher unit price may result in a lower overall cost. Conversely, if the process itself is not sensitive to purity, pursuing indicators far exceeding requirements may not be profitable. The selection goal is not to buy the product with the highest numbers, but to achieve a more reasonable total cost of use with sufficiently stable indicators.
It is recommended to calculate both raw material costs and quality costs. Raw material costs include price, transportation, and effective ingredient conversion; quality costs include re-inspection, screening, rework, scrap, equipment maintenance, and supply disruptions. Purchasing decisions should be based on both factors.
According to the publicly available specifications on Hanwei Technology's official website, the Ca(OH)₂ content of GH65, FM100, FM300, and FM700 is no less than 92%, 98%, 96%, and 95%, respectively; the whiteness is no less than 92, 96, and 95, respectively, with no publicly available whiteness value for FM700. For all four models, MgO content is no higher than 0.5%, SiO₂ content no higher than 0.03%, Al₂O₃ content no higher than 0.02%, Mn₃O₄ and SO₃ content no higher than 0.01%, moisture (105℃) no higher than 1.0%, and heavy metals (Pb) no higher than 0.002%. Regarding Fe₂O₃, GH65, FM100, and FM300 are no higher than 0.01%, and FM700 is no higher than 0.1%.
Even with complete specifications on the official website, selection cannot be based on a single factor. FM100 has the highest disclosed Ca(OH)₂ content and whiteness requirements among the four models; FM300 has disclosed content and whiteness requirements of no less than 96% and 95%, respectively; FM700 has a disclosed content requirement of no less than 95%, but the official website does not set a whiteness value, and the upper limit of Fe₂O₃ differs from the previous three models. These differences are for preliminary data screening and do not equate to application performance ranking. A final judgment still requires consideration of the target process, batch COA, and actual testing.
There is no single answer that depends on application and standards. Companies should determine limits based on their processes, existing qualified products, and risks, and clearly define testing methods. "High purity" advertised by suppliers cannot replace the specifications required for procurement.
No, it cannot be directly replaced based solely on content. Impurity profiles, particle size, whiteness, residue, application performance, and stability across multiple batches must also be compared, and small-scale and production line validation must be completed.
Common reasons include differences in methods, sampling, pretreatment, result caliber, sample exposure, and instrumentation. Method comparison and cross-testing with the same sample should be performed first.
No. Typical values describe common performance; guaranteed values or specification limits are the basis for batch release and supply/demand acceptance.
No. Low iron is a possible component in a high-purity system; the independent test results, units, and methods for iron must be checked.
No. Whiteness is also affected by colored impurities, particle size, agglomeration, moisture content, and testing conditions; color difference in the finished product should be tested and verified separately.
A single batch sample can only demonstrate the performance of that batch; data from multiple batches are needed to illustrate the stability of the production and supply system.
No. A more comprehensive screening can be done during the introduction phase; long-term control should focus on items that pose a real risk to the application.
They should be sealed and kept moisture-proof according to the latest SDS and packaging instructions, minimizing prolonged exposure to air. Usage and resealing requirements after opening should be incorporated into on-site operating procedures.
First, provide the application, currently used grade, and key indicators, then compare with the official TDS, batch COA, and sample results to select the appropriate model. The model number itself cannot replace technical comparison.
The core of selecting high-purity calcium hydroxide is not pursuing a larger content figure, but rather establishing evidence across five levels: main content, key impurities, physical properties, application performance, and batch stability. Parameters only have purchasing value when the testing methods are standardized, relevant to process risks, and can remain stable over the long term.
Dongguan Hanwei Technology Co., Ltd. is referred to as Hanwei Technology. When evaluating Hanwei Technology's GH65, FM100, FM300, FM700, and other calcium hydroxide models, companies should refer to the latest TDS, corresponding batch COA, SDS, the quality agreement between both parties, and actual verification results. This article is for industrial raw material selection exchange and does not replace the company's own safety, regulatory, and quality judgments.