Regeneration Mechanism and Value-Creating Outputs
The HpM steelmaking sludge and dust regeneration technology is an essentially mechanical process based on the action of high-energy micro- and nano-scale vacuum bubbles. These bubbles promote the controlled disaggregation of particulate materials, enabling the selective liberation and recovery of both metallic and oxide phases originally embedded within steelmaking residues.
Within this process, HpM produces two distinct value-added outputs: BAP Steel, derived from the Portuguese term Briquete de Aço Puro (Pure Steel Briquette), and ACO Iron, an acronym for Aglomerado Circular de Óxidos (Circular Oxides Agglomerate). BAP Steel is a high-metallicity product designed to be reused as premium scrap directly in BOF, AOD or Electric Arc Furnaces (EAF). ACO Iron, in turn, extends beyond a product generated from fine sludge, functioning as a regeneration platform capable of integrating multiple oxide-bearing residues across the steel mill value chain.
The HpM process is structured into two distinct stages. The first stage is dedicated to the recovery of metallic content from coarse steelmaking sludge or coarse dust collected from electrostatic precipitators (coarse ESP dust). During this stage, the coarse fraction is disaggregated, releasing steel microspheres that are originally encapsulated within iron oxides, limestone, alkalis and zinc oxide phases. Owing to the significantly higher density of metallic steel relative to these oxides, the liberated steel particles are subsequently separated and concentrated using gravimetric techniques.
This concentrated steel powder is then directed to a powder metallurgy route specifically developed by HpM for this application. Through a low-temperature agglomeration process—operating well below the melting point of steel and without the use of binders—the material is shaped into steel briquettes. The resulting product is designated BAP Steel.
The non-metallic material separated from the coarse fraction is subsequently combined with the finer particulate fraction, and both streams are subjected to further treatment in the second stage of the process. This stage focuses on reducing excess limestone content and lowering alkali and zinc oxide levels. Zinc removal is feasible when zinc is present in the form of zinc oxide; however, when zinc occurs as zinc ferrite (with the general formula ZnₓFe₃₋ₓO₄), it cannot be effectively removed. This distinction is assessed during the preliminary characterization phase prior to process implementation and may influence the most appropriate reuse pathway for the treated material. In most cases, zinc oxide reduction to acceptable levels enables reuse in blast furnace operations.
Once contaminant levels are reduced, both the treated non-metallic coarse fraction and the fine fraction are directed to a binder-free agglomeration step. Depending on operational requirements, this step may involve pelletizing or briquetting. The resulting product is an iron-oxide-rich agglomerate with low contaminant levels, designated ACO Iron.
Beyond the treatment of steelmaking sludge and ESP dust, ACO Iron represents a broader regeneration platform for oxide-based residues generated throughout the steel mill. As this phase of the HpM process is specifically designed to recover and condition oxide materials through contaminant reduction, other iron-bearing residues can be incorporated into the ACO Iron stream, provided they meet defined technical criteria. These include residues treated by HpM’s oil-removal process, materials recovered from landfills, fine residues from agglomeration operations such as pellet fines (from pellet production or pellet washing prior to direct reduction), iron ore fines, sinter fines, blast furnace sludges and other blast furnace fines.
By integrating these multiple residue streams into a single regeneration route, the ACO Iron process forms a comprehensive Circular Economy loop with enhanced leakage-prevention capability. This unified approach links several steel mill process residues into a single system aimed at maximizing the reuse of materials already purchased, processed and handled by the steel mill, thereby improving resource efficiency, reducing waste generation and strengthening the overall circularity of steelmaking operations.
Metallic Content Recovery from Corase Sludge / Dust
1 - Coarse Sludge / Dust Disaggregation Process
2 - Metallic Separation Process
(A) Coarse Sludge "In Natura"
Magnification: 1,200 x
(C) Disaggregated Coarse Sludge
Magnification: 1,200 x
(E) Steel Isolated Microspheres
Magnification: 1,200 x
(F) Oxides and Non Metallic Particles
Magnification: 1,200 x
(B) Micro/Nano Vaccum Bubles
Generator Device (CVBD)
(D) Special Designed
Humphrey Type
Spiral
3 - Vacuum Bubbles Disaggregation Process Phases - Illustration
(G)
Coarse Sludge Slurry
(H)
Disaggregation Phases
H.1
H.2
H.3
(J) Oxides and
non metallic Particles
(I) Steel
Microspheres
The HpM process combines vacuum bubble-induced disaggregation with gravimetric separation to recover metallic content from coarse steelmaking sludge.
Microstructural analysis at 1,200× magnification shows the transformation from heavily contaminated sludge, Image (A) and Image (G), to fully liberated steel microspheres after treatment with micro and nano vacuum bubbles generated by the CVBD device, Image (C) and Image (H.3).
Once liberated, metallic and oxidized phases are efficiently separated using a specially designed Humphrey-type spiral, Image (D), producing clean steel microspheres, Image (E) and Image (I), and an iron-rich oxide fraction also containing limestone, zinc and alkalis, Image (F) and Image (J).
BAP Steel – Binder-Free Solid-State Powder Metallurgy
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(K) Steel Microspheres (Steel Powder)
(L) Non-Binder Steel Briquettes
BAP Steel
(M) BAP Steel Special
Powder Metallugy
(N) BAP Steel
Final Product
Steel microspheres isolated after coarse sludge or ESP dust disaggregation are dried and conveyed to storage silos, as shown in Image (K), where the metallic brightness of the steel powder can be observed.
The steel powder is then directed to an HpM-adapted briquetting process, specifically designed to produce binder-free steel briquettes, Image (L). After briquetting, the material undergoes a controlled solid-state powder metallurgy process, at temperatures well below the steel melting point, Image (M).
This process applies a specific sequence of heating and cooling cycles, promoting solid-state bonding between microspheres, increasing the mechanical strength of BAP Steel while minimizing fines generation, resulting in the final product shown in Image (N).
Oxides Decontamination and ACO Iron Production
(O) Micro/Nano Vaccum Bubles
Fine Sludge Reactor (CVB-SR)
(P) Vacuum Filter
(Q) Clean Fine Sludge
Pelletizing - ACO Iron
(R) Clean Fine Sludge
Briquetting - ACO Iron
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Non-metallic fractions recovered from coarse steelmaking sludge or ESP dust are combined with fine steelmaking sludge or fine ESP dust and processed in a continuous micro- and nano-vacuum bubble reactor, operating under controlled conditions tailored to the specific behavior of each fine residue, as illustrated in Image (O).
After treatment, the material is submitted to vacuum filtration for contaminant removal and moisture adjustment, Image (P). Once suitable physical conditions are achieved, the clean iron-rich oxide material may be directed either to pelletizing, Image (Q), or to briquetting, Image (R), resulting in ACO Iron — a circular iron oxide agglomerate designed for reduction processes.